WorldWideScience

Sample records for electronically excited molecules

  1. Electron-excited molecule interactions

    International Nuclear Information System (INIS)

    Christophorou, L.G.; Tennessee Univ., Knoxville, TN

    1991-01-01

    In this paper the limited but significant knowledge to date on electron scattering from vibrationally/rotationally excited molecules and electron scattering from and electron impact ionization of electronically excited molecules is briefly summarized and discussed. The profound effects of the internal energy content of a molecule on its electron attachment properties are highlighted focusing in particular on electron attachment to vibrationally/rotationally and to electronically excited molecules. The limited knowledge to date on electron-excited molecule interactions clearly shows that the cross sections for certain electron-molecule collision processes can be very different from those involving ground state molecules. For example, optically enhanced electron attachment studies have shown that electron attachment to electronically excited molecules can occur with cross sections 10 6 to 10 7 times larger compared to ground state molecules. The study of electron-excited molecule interactions offers many experimental and theoretical challenges and opportunities and is both of fundamental and technological significance. 54 refs., 15 figs

  2. Electron attachment to excited molecules

    International Nuclear Information System (INIS)

    Christophorou, L.G.; Pinnaduwage, L.A.; Datskos, P.G.

    1993-01-01

    Studies on electron attachment to molecules rotationally/vibrationally excited thermally or via infrared-laser excitation showed that the effect of internal energy of a molecule on its electron attachment properties depends on the mode--dissociative or nondissociative--of electron attachment. They quantified the effect of the internal energy of the molecule on the rate of destruction (by autodissociation or by autodetachment) of its parent transient anion. Generally, increases in ro-vibrational molecular energy increase the cross section for dissociative electron attachment and decrease the effective cross section for parent anion formation due mainly to increased autodetachment. These findings and their understanding are discussed. A discussion is given, also, of recent investigations of electron attachment to electronically excited molecules, especially photoenhanced dissociative electron attachment to long- and short-lived excited electronic states of molecules produced directly or indirectly by laser irradiation. These studies showed that the cross sections for dissociative electron attachment to electronically excited molecules usually are many orders of magnitude larger than those for the ground-state molecules. The new techniques that have been developed for such studies are briefly described also

  3. Infrared emission from electronically excited biacetyl molecules

    NARCIS (Netherlands)

    Drent, E.; Kommandeur, J.

    1971-01-01

    The infrared emission of electronically excited biacetyl molecules in the gas phase at low pressure was observed. Some experimental details are given, and it is shown that the emission derives from biacetyl molecules in their triplet state. The emission is dependent on the wavelength of excitation.

  4. Rotational excitation of molecules by electron collisions

    International Nuclear Information System (INIS)

    Itikawa, Yukikazu; Mason, Nigel

    2005-01-01

    The anisotropic charge distribution of a molecule can easily induce a rotational transition in the molecule during an electron collision. Further, since the level spacing of the rotational states is very small, the transition can take place over a wide range of electron energies. The rotational excitation is the dominant energy-loss process for an electron in a molecular gas, when the electron energy lies below the vibrational threshold of the molecule. In the case of polar molecules, the rotationally excited molecule promptly emits microwave (or far infrared) radiation. In this way, the rotational excitation effectively cools electrons. The present paper reviews theoretical and experimental studies of the electron-impact rotational excitation of molecules. After a general introduction of the relevant theory and experiment, case studies of five different molecular species (H 2 , N 2 , CH 4 , HCl, and H 2 O) are presented to show the characteristics of rotational cross sections. From those studies, common features of the cross sections are discussed

  5. Reaction dynamics of electronically excited alkali atoms with simpler molecules

    International Nuclear Information System (INIS)

    Weiss, P.S.; Mestdagh, J.M.; Schmidt, H.; Vernon, M.F.; Covinsky, M.H.; Balko, B.A.; Lee, Y.T.

    1985-05-01

    The reactions of electronically excited sodium atoms with simple molecules have been studied in crossed molecular beams experiments. Electronically excited Na(3 2 P/sub 3/2/, 4 2 D/sub 5/2/, and 5 2 S/sub 1/2/) were produced by optical pumping using single frequency dye lasers. The effects of the symmetry, and the orientation and alignment of the excited orbital on the chemical reactivity, and detailed information on the reaction dynamics were derived from measurements of the product angular and velocity distributions. 12 refs., 9 figs

  6. Electron-driven excitations and dissociation of molecules

    Energy Technology Data Exchange (ETDEWEB)

    Miller, Greg [Univ. of California, Davis, CA (United States); Orel, Ann E. [Univ. of California, Davis, CA (United States)

    2015-02-13

    This program studied how energy is interchanged in electron and photon collisions with molecules leading to ex-citation and dissociation. Modern ab initio techniques, both for the photoionization and electron scattering, and the subsequent nuclear dynamics studies, are used to accurately treat these problems. This work addresses vibrational ex-citation and dissociative attachment following electron impact, and the dynamics following inner shell photoionzation. These problems are ones for which a full multi-dimensional treatment of the nuclear dynamics is essential and where non-adiabatic effects are expected to be important.

  7. Electronic excitation of atoms and molecules by electron impact in a linear algebraic, separable potential approach

    International Nuclear Information System (INIS)

    Collins, L.A.; Schneider, B.I.

    1984-01-01

    The linear algebraic, separable potential approach is applied to the electronic excitation of atoms and molecules by electron impact. By representing the exchange and off-diagonal direct terms on a basis, the standard set of coupled inelastic equations is reduced to a set of elastic inhomogeneous equations. The procedure greatly simplifies the formulation by allowing a large portion of the problem to be handled by standard bound-state techniques and by greatly reducing the order of the scattering equations that must be solved. Application is made to the excitation of atomic hydrogen in the three-state close-coupling (1s, 2s, 2p) approximation. (author)

  8. Excitation and dissociation of molecules by low-energy (0-15 eV) electrons

    International Nuclear Information System (INIS)

    Verhaart, G.J.

    1980-01-01

    The author deals with excitation and dissociation processes which result from the interaction between low-energy (0.15 eV) electrons and molecules. Low-energy electron-impact spectroscopy is used to gain a better knowledge of the electronic structure of halomethanes, ethylene and some of its halogen substituted derivatives, and some more complex organic molecules. (Auth.)

  9. Visualizing rotational wave functions of electronically excited nitric oxide molecules by using an ion imaging technique.

    Science.gov (United States)

    Mizuse, Kenta; Chizuwa, Nao; Ikeda, Dai; Imajo, Takashi; Ohshima, Yasuhiro

    2018-01-31

    Here we report the dissociative ionization imaging of electronically excited nitric oxide (NO) molecules to visualize rotational wave functions in the electronic excited state (A 2 Σ + ). The NO molecules were excited to a single rotational energy eigenstate in the first electronic excited state by a resonant nanosecond ultraviolet pulse. The molecules were then irradiated by a strong, circularly polarized femtosecond imaging pulse. Spatial distribution of the ejected N + and O + fragment ions from the dissociative NO 2+ was recorded as a direct measure of the molecular axis distribution using a high-resolution slice ion imaging apparatus. The circularly polarized probe pulse realizes the isotropic ionization and thus undistorted shapes of the functions can be visualized. Due to the higher ionization efficiency of the excited molecules relative to the ground state ones, signals from the excited NO were enhanced. We can, therefore, extract shapes of the square of rotational wave functions in the electronic excited state although the unexcited ground state molecules are the majority in an ensemble. The observed images show s-function-like and p-function-like shapes depending on the excitation wavelengths. These shapes well reflect the rotational (angular momentum) character of the prepared states. The present approach directly leads to the evaluation method of the molecular axis alignment in photo-excited ensembles, and it could also lead to a visualization method for excited state molecular dynamics.

  10. Multiple scattering approach to the vibrational excitation of molecules by slow electrons

    International Nuclear Information System (INIS)

    Drukarev, G.

    1976-01-01

    Another approach to the problem of vibrational excitation of homonuclear two-atomic molecules by slow electrons possibly accompanied by rotational transitions is presented based on the picture of multiple scattering of an electron inside the molecule. The scattering of two fixed centers in the zero range potential model is considered. The results indicate that the multiple scattering determines the order of magnitude of the vibrational excitation cross sections in the energy region under consideration even if the zero range potential model is used. Also the connection between the multiple scattering approach and quasi-stationary molecular ion picture is established. 9 refs

  11. Investigation of Multiconfigurational Short-Range Density Functional Theory for Electronic Excitations in Organic Molecules

    DEFF Research Database (Denmark)

    Hubert, Mickaël; Hedegård, Erik D.; Jensen, Hans Jørgen Aa

    2016-01-01

    inadequate when the molecule has near-degeneracies and/or low-lying double-excited states. To address these issues we have recently proposed multiconfiguration short-range density-functional theory-MC-srDFT-as a new tool in the toolbox. While initial applications for systems with multireference character......Computational methods that can accurately and effectively predict all types of electronic excitations for any molecular system are missing in the toolbox of the computational chemist. Although various Kohn-Sham density-functional methods (KS-DFT) fulfill this aim in some cases, they become......-srDFT for a selected benchmark set of electronic excitations of organic molecules, covering the most common types of organic chromophores. This investigation confirms the expectation that the MC-srDFT method is accurate for a broad range of excitations and comparable to accurate wave function methods such as CASPT2...

  12. Electronic excited states of Si(100) and organic molecules adsorbed on Si(100).

    Science.gov (United States)

    Besley, Nicholas A; Blundy, Adam J

    2006-02-02

    The electronically excited states of the Si(100) surface and acetylene, benzene, and 9,10-phenanthrenequinone adsorbed on Si(100) are studied with time-dependent density functional theory. The computational cost of these calculations can be reduced through truncation of the single excitation space. This allows larger cluster models of the surface in conjunction with large adsorbates to be studied. On clean Si(100), the low-lying excitations correspond to transitions between the pi orbitals of the silicon-silicon dimers. These excitations are predicted to occur in the range 0.4-2 eV. When organic molecules are adsorbed on the surface, surface --> molecule, molecule --> surface, and electronic excitations localized within the adsorbate are also observed at higher energies. For acetylene and benzene, the remaining pipi* excitations are found to lie at lower energies than in the corresponding gas-phase species. Even though the aromaticity of 9,10-phenanthrenequinone is retained, significant shifts in the pipi* excitations of the aromatic rings are predicted. This is in part due to structural changes that occur upon adsorption.

  13. Enhanced Electron Attachment to Highly-Excited Molecules and Its Applications in Pulsed Plasmas

    International Nuclear Information System (INIS)

    Ding, W.X.; Ma, C.Y.; McCorkle, D.L.; Pinnaduwage, L.A.

    1999-01-01

    Studies conducted over the past several years have shown that electron attachment to highly-excited states of molecules have extremely large cross sections. We will discuss the implications of this for pulsed discharges used for H - generation, material processing, and plasma remediation

  14. Bibliography on electron collisions with molecules: rotational and vibrational excitations, 1980-2000

    Energy Technology Data Exchange (ETDEWEB)

    Itikawa, Yukikazu [Institute of Space and Astronautical Science, Sagamihara, Kanagawa (Japan)

    2001-04-01

    A list of papers reporting cross sections for electron-impact excitations of rotational and vibrational states of molecules is presented. The list includes both the theoretical and the experimental papers published in 1980-2000. An index by molecular species is provided at the end of the bibliography. (author)

  15. Antibonding intermediate state in the theory of vibrational excitation of diatomic molecules by slow electrons

    International Nuclear Information System (INIS)

    Kazanskii, A.K.

    1982-01-01

    An exactly solvable model is constructed for the description of the processes that take place when a slow electron collides with a diatomic molecule (vibrational excitation, associative detachment, and dissociative attachment). As a particular model of the variant, the case of an antibonding (virtual) state of an intermediate state is considered, and a term of this state is parametrized in a very simple manner. The vibrational excitation and dissociative attachment are calculated for a system corresponding to the HCl molecule. The results are in good qualitative agreement with experiment

  16. Surface chemical reactions induced by molecules electronically-excited in the gas

    DEFF Research Database (Denmark)

    Petrunin, Victor V.

    2011-01-01

    and alignment are taking place, guiding all the molecules towards the intersections with the ground state PES, where transitions to the ground state PES will occur with minimum energy dissipation. The accumulated kinetic energy may be used to overcome the chemical reaction barrier. While recombination chemical...... beams inducing the reaction can be used to distinguish the new process we try to investigate from chemical reactions induced by photoexcitation within adsorbed molecules and/or gas phase photolysis.......We present a model suggesting high chemical activity of electronically-excited molecules colliding with an isolator surface. Initial photochemical event is accounted for as the result of molecular evolution on the electronically-excited potential energy surface (PES), where acceleration...

  17. Influence of excited molecules on electron swarm transport coefficients and gas discharge kinetics

    International Nuclear Information System (INIS)

    Petrovic, Z.L.; Jovanovic, J.V.; Raspopovic, Z.M.; Bzenic, S.A.; Vrhovac, S.B.

    1997-01-01

    In this paper we study different effects of excited molecules on swarm parameters, electron energy distribution functions and gas discharge modeling. First we discuss a possible experiment in parahydrogen to resolve the discrepancy in hydrogen vibrational excitation cross section data. Negative differential conductivity (NDC) is a kinetic phenomenon which manifests itself in a particular dependence of the drift velocity on E=N and it is affected by superelastic collisions with excited states. A complete kinetic scheme for argon required to model excited state densities in gas discharges is also described. These results are used to explain experiments in capacitively and inductively coupled RF plasmas used for processing. The paper illustrates the application of atomic and molecular collision data, swarm data and the theoretical techniques in modeling of gas discharges with large abundances of excited molecules. It is pointed out that swarm experiments with excited molecules are lacking and that there is a shortage of reliable data, while the numerical procedures are sufficiently developed to include all the important effects. (authors). 59 refs., 12 figs

  18. Cross section data for electron-impact inelastic processes of vibrationally excited molecules of hydrogen and its isotopes

    CERN Document Server

    Celiberto, R; Laricchiuta, A; Capitelli, M; Wadehra, J M; Atems, D E

    2001-01-01

    An extensive cross section database for the electron-impact inelastic processes of vibrationally excited molecules of hydrogen and its isotopes is presented. The following inelastic processes are covered: electronic excitation (dissociative and nondissociative), direct ionization (dissociative and nondissociative), excitation-radiative decay vibrational excitation and dissociation, and dissociative electron attachment. The data have been compiled partly from the literature and partly generated theoretically for the present report. The data are presented in graphical form. The data are also presented by sufficiently accurate analytic fit functions. Mass-scaling relations are provided for cross section evaluation of those isotope molecules for which calculated data are not available.

  19. Analysis of Excitation and Ionization of Atoms and Molecules by Electron Impact

    CERN Document Server

    Chaudhry, Afzal

    2011-01-01

    Analysis of Excitation and Ionization of Atoms and Molecules by Electron Impact, by Afzal Chaudhry and Hans Kleinpoppen, describes in detail the measurements of the partial and total doubly differential cross sections for the multiple-ionization of rare gas atoms by electron impact. These measurements show, among other trends, the role of Auger transitions in the production of multiply ionized atoms in the region where the incident electron energy is sufficient to produce inner shell ionization. Other processes like Coster-Kronig transitions and shake off also contribute towards increasing the charge of the ions. As discussed in the book, an incident electron having energy of 6 keV, for example, in a collision with xenon atom can remove up to nine electrons! The measurements of doubly differential cross sections for the dissociative and non-dissociative ionization of hydrogen, sulfur dioxide and sulfur hexa fluoride molecular gases are also explored. The results of the measurements for the sulfur dioxide mole...

  20. Time delay for resonant vibrational excitation in electron--molecule collisions

    International Nuclear Information System (INIS)

    Gauyacq, J.P.

    1990-01-01

    An analysis of the time delay associated with vibrational excitation in electron--molecule collision is presented. It consists of a direct study of the time dependence of the process for three model systems. An electron wave packet, that is narrow in time, is sent on the target and the amplitudes in the different inelastic channels are studied as functions of time. The time delay is found to correspond to very different time effects: broadenings, shifts in time of the wave packet, but also complex distortions that cannot be represented by a time delay. The direct analysis of the scattered wave also provides new insights into the vibrational excitation process. It should be a useful tool to analyze complex collision processes

  1. The estimation of the G-values for ionization and excitation of ten-electron molecules

    International Nuclear Information System (INIS)

    Okazaki, Kiyoshi; Sato, Shin; Ohno, Shin-ichi.

    1976-01-01

    The binary-encounter collision theory is applied to calculate the G-values for the ionization and excitation of methane, ammonia, and water irradiated by 100 keV electrons. Double collision of the incident electron in a molecule is also taken into account. On the assumption of the occurrence of certain reactions in the systems, the G-values for electrons, various radicals, and several final products were estimated. Some of the results are as follows: the G-values for electrons were 3.60 for methane, 3.56 for ammonia, and 3.00 for water. These values are in fair agreement with the experimental values: 3.6 for methane, 3.8 for ammonia, and 3.3 for water. The calculated G-value for hot hydrogen atoms was about 1.0 for all three compounds. The ratios of the G-value for excitation to that for electons are 1.1 for methane, 1.5 for ammonia, and 1.7 for water. An estimation was also made of the G-value for the emission of highly-excited hydrogen atoms using reported cross sections. The G-values are 0.1 for methane and ammonia, and 0.2 for water. (auth.)

  2. Selective excitation of a vibrational level within the electronic ground state of a polyatomic molecule with ultra pulses

    CSIR Research Space (South Africa)

    de Clercq, L

    2010-09-01

    Full Text Available Coherent control of the upper vibrational level populations in the electronic ground state of a polyatomic molecule was simulated. Results indicate that selective excitation of a specific upper state level is possible...

  3. Selective excitation of a vibrational level within the electronic ground state of a polyatomic molecule with ultra short pulses

    CSIR Research Space (South Africa)

    De Clercq, L

    2010-09-01

    Full Text Available Coherent control of the upper vibrational level populations in the electronic ground state of a polyatomic molecule was simulated. Results indicate that selective excitation of a specific upper state level is possible....

  4. High Resolution UV Emission Spectroscopy of Molecules Excited by Electron Impact

    Science.gov (United States)

    James, G. K.; Ajello, J. M.; Beegle, L.; Ciocca, M.; Dziczek, D.; Kanik, I.; Noren, C.; Jonin, C.; Hansen, D.

    1999-01-01

    Photodissociation via discrete line absorption into predissociating Rydberg and valence states is the dominant destruction mechanism of CO and other molecules in the interstellar medium and molecular clouds. Accurate values for the rovibronic oscillator strengths of these transitions and predissociation yields of the excited states are required for input into the photochemical models that attempt to reproduce observed abundances. We report here on our latest experimental results of the electron collisional properties of CO and N2 obtained using the 3-meter high resolution single-scattering spectroscopic facility at JPL.

  5. High mass-resolution electron-ion-ion coincidence measurements on core-excited organic molecules

    CERN Document Server

    Tokushima, T; Senba, Y; Yoshida, H; Hiraya, A

    2001-01-01

    Total electron-ion-ion coincidence measurements on core excited organic molecules have been carried out with high mass resolution by using multimode (reflectron/linear) time-of-flight mass analyzer. From the ion correlation spectra of core excited CH sub 3 OH and CD sub 3 OH, the reaction pathway to form H sub 3 sup + (D sub 3 sup +) is identified as the elimination of three H (D) atoms from the methyl group, not as the inter-group (-CH sub 3 and -OH) interactions. In a PEPIPICO spectrum of acetylacetone (CH sub 3 COCH sub 2 COCH sub 3) measured by using a reflectron TOF, correlations between ions up to mass number 70 with one-mass resolution was recorded.

  6. Dissociative electron attachment to vibrationally excited H2 molecules involving the 2Σg+ resonant Rydberg electronic state

    International Nuclear Information System (INIS)

    Celiberto, R.; Janev, R.K.; Wadehra, J.M.; Tennyson, J.

    2012-01-01

    Graphical abstract: Dissociative electron attachment cross sections as a function of the incident electron energy and for the initial vibration levels v i = 0–5, 10 of the H 2 molecule. Highlights: ► We calculated electron–hydrogen dissociative attachment cross sections and rates coefficients. ► Collision processes occurring through a resonant Rydberg state are considered. ► Cross sections and rates were obtained for vibrationally excited hydrogen molecules. ► The cross sections exhibit pronounced oscillatory structures. ► A comparison with the process involving the electron–hydrogen resonant ground state is discussed. - Abstract: Dissociative electron attachment cross sections (DEA) on vibrationally excited H 2 molecule taking place via the 2 Σ g + Rydberg-excited resonant state are studied using the local complex potential (LCP) model for resonant collisions. The cross sections are calculated for all initial vibrational levels (v i = 0–14) of the neutral molecule. In contrast to the previously noted dramatic increase in the DEA cross sections with increasing v i , when the process proceeds via the X 2 Σ u + shape resonance of H 2 , for the 2 Σ g + Rydberg resonance the cross sections increase only gradually up to v i = 3 and then decrease. Moreover, the cross sections for v i ⩾ 6 exhibit pronounced oscillatory structures. A discussion of the origin of the observed behavior of calculated cross sections is given. The DEA rate coefficients for all v i levels are also calculated in the 0.5–1000 eV temperature range.

  7. Non-equilibrium kinetics of plasma-assisted combustion: the role of electronically excited atoms and molecules

    Science.gov (United States)

    Popov, Nikolay

    2016-09-01

    A review of experimental and theoretical investigations of the effect of electronically excited atoms and molecules on the induction delay time and on the shift of the ignition temperature threshold of combustible mixtures is presented. At relatively low initial gas temperature, the effect of excited O(1D) atoms on the oxidation and reforming of combustible mixtures is quite significant due to the high rates of reactions of O(1D) atoms with hydrogen and hydrocarbon molecules. The singlet oxygen molecules, O2(a1Δg) , participate both in chain initiation and chain branching reactions, but the effect of O2(a1Δg) in the ignition processes is generally less important compared to the oxygen atoms. To reduce the ignition delay time and decrease the temperature threshold of fuel-air mixtures, the use of gas discharges with relatively high E/N values is recommended. In this case the reactions of electronically excited N2(A3Σu+ , B3πg , C3πu , a'1Σu-) molecules, and atomic particles in ground and electronically excited states are extremely important. The energy stored in electronic excitation of atoms and molecules is spent on the additional dissociation of oxygen and fuel molecules, on the fast gas heating, and finally to the triggering of chain branching reactions. This work was partially supported by AOARD AFOSR, FA2386-13-1-4064 grant and Linked International Laboratory LIA KaPPA (France-Russia).

  8. Electronic excitation and deexcitation of atoms and molecules in nonequilibrium plasmas; Hiheiko plasma chu no denshi reiki ryushi hanno katei

    Energy Technology Data Exchange (ETDEWEB)

    Shimamori, H. [Fukui University of Technology, Fukui (Japan)

    1997-05-20

    Regarding excitation and deexcitation due to collision of electrons and deexcitation due to collision of baryons in nonequilibrium plasma, explanation is made about the general characteristics of the elementary processes involving their formation and disappearance and about the prediction of their sectional areas and velocity constants. As for the process of the formation of excited atoms and molecules by collision of electrons, it may be divided into the direct excitation in the ground state, excitation and light emission toward the resonance state, reexcitation and transformation of excited particles, recombination of electrons and positive atomic ions, and dissociation and recombination of electrons and positive molecular ions. As for the process of the disappearance of excited particles, there exist various courses it may follow, and it is quite complicated because it is dependent on the types of particles involved and the conditions the process proceeds under. Although the skeleton has been built of the theory of derivation of the sectional area of excitation due to collision of electrons and atoms/molecules, yet it is accurate enough only when applied to simple atomic/molecular systems, is far from satisfying in general, and is to be augmented by data from future experiments. 22 refs., 3 figs., 1 tab.

  9. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    Science.gov (United States)

    Egidi, Franco; Segado, Mireia; Koch, Henrik; Cappelli, Chiara; Barone, Vincenzo

    2014-12-01

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π*, π-π*, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  10. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    Energy Technology Data Exchange (ETDEWEB)

    Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it [Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56126 Pisa (Italy); Koch, Henrik [Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Cappelli, Chiara [Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via G. Moruzzi, 3 I-56124 Pisa (Italy)

    2014-12-14

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  11. Influence of temperature on the selectivity of dissociation of CF3I molecules by multiphoton vibrational and subsequent electronic excitation

    International Nuclear Information System (INIS)

    Kudryavtsev, Y.A.

    1980-01-01

    A report is given of theoretical and experimental studies of the influence of temperature on the selectivity of separating carbon isotopes by multiphoton vibrational and subsequent electronic excitation of CF 3 I molecules. Carbon dioxide laser radiation was used for vibrational excitation and XeC1 and XeF excimer lasers were used for dissociation. A selectivity of 108 was achieved at 223 0 K

  12. Carbon K-shell excitation in small molecules by high-resolution electron impact

    International Nuclear Information System (INIS)

    Tronc, M.; King, G.C.; Read, F.H.

    1979-01-01

    The excitation of 1s carbon electrons has been observed in C0, CH 4 , CF4, C0 2 , COS, C 2 H 2 and C 2 H 4 by means of the electron energy-loss technique with high resolution (70 meV in the 300 eV excitation energy range) and at an incident electron energy of 1.5 keV. The energies, widths and vibrational structures of excited states corresponding to the promotion of 1s carbon electrons to unoccupied valence and Rydberg orbitals have been obtained. The validity of the equivalent-core model, and the role of resonances caused by potential barriers, are discussed. (author)

  13. Matrix photochemistry of small molecules: Influencing reaction dynamics on electronically excited hypersurfaces

    Energy Technology Data Exchange (ETDEWEB)

    Laursen, S.L.

    1990-01-01

    Investigations of chemical reactions on electronically excited reaction surfaces are presented. The role of excited-surface multiplicity is of particular interest, as are chemical reactivity and energy transfer in systems in which photochemistry is initiated through a metal atom sensitizer.'' Two approaches are employed: A heavy-atom matrix affords access to forbidden triplet reaction surfaces, eliminating the need for a potentially reactive sensitizer. Later, the role of the metal atom in the photosensitization process is examined directly.

  14. Matrix photochemistry of small molecules: Influencing reaction dynamics on electronically excited hypersurfaces

    International Nuclear Information System (INIS)

    Laursen, S.L.

    1990-01-01

    Investigations of chemical reactions on electronically excited reaction surfaces are presented. The role of excited-surface multiplicity is of particular interest, as are chemical reactivity and energy transfer in systems in which photochemistry is initiated through a metal atom ''sensitizer.'' Two approaches are employed: A heavy-atom matrix affords access to forbidden triplet reaction surfaces, eliminating the need for a potentially reactive sensitizer. Later, the role of the metal atom in the photosensitization process is examined directly

  15. Inner shell excitation in atoms and molecules by high resolution electron impact

    International Nuclear Information System (INIS)

    King, G.C.

    1986-01-01

    In this work an inner-shell spin-forbidden transition in N 2 and a parity-forbidden transition in Ar were studied. These transitions were observed by using incident electron energies as low as 1.15 times the excitation energy of the inner-shell states. (Auth.)

  16. Ejection of molecules from solid deuterium excited by keV electrons

    DEFF Research Database (Denmark)

    Pedrys, R.; Warczak, B.; Schou, Jørgen

    1997-01-01

    The energy distribution of sputtered D-2 from electron-bombarded solid deuterium has been studied for the first time. The spectra from this quantum solid show features that may originate from an energy release sequence of association of atoms. For ejection energies above 1 meV the gross features...... of the spectrum are similar to those from electronic sputtering of ether much less volatile condensed gases. Sputtered D-4 molecules have been observed for the first time as well....

  17. Calculation of Ground State Rotational Populations for Kinetic Gas Homonuclear Diatomic Molecules including Electron-Impact Excitation and Wall Collisions

    International Nuclear Information System (INIS)

    Farley, David R.

    2010-01-01

    A model has been developed to calculate the ground-state rotational populations of homonuclear diatomic molecules in kinetic gases, including the effects of electron-impact excitation, wall collisions, and gas feed rate. The equations are exact within the accuracy of the cross sections used and of the assumed equilibrating effect of wall collisions. It is found that the inflow of feed gas and equilibrating wall collisions can significantly affect the rotational distribution in competition with non-equilibrating electron-impact effects. The resulting steady-state rotational distributions are generally Boltzmann for N (ge) 3, with a rotational temperature between the wall and feed gas temperatures. The N = 0,1,2 rotational level populations depend sensitively on the relative rates of electron-impact excitation versus wall collision and gas feed rates.

  18. Initial mechanisms for the dissociation of carbon from electronically-excited nitrotoluene molecules

    Science.gov (United States)

    Yuan, Bing; Eilers, Hergen

    2017-12-01

    We calculated the photoinduced decomposition of various nitrotoluene molecules, resulting in the formation of atomic carbon, at the B3LYP/6-311++G(d,p) level of theory using Gaussian 09. In addition, we used TD-DFT (B3LYP/6-311++G(d,p)) to calculate the excitation energies. The results confirm our previously reported experimental results. Specifically, we show that the absorption of 226 nm (5.49 eV) light can lead to the decomposition of nitrotoluene molecules and the formation of atomic carbon. One 226 nm photon is sufficient for the dissociation of carbon from 2-NT and 4-NT molecules. During the dissociation process, the CH3 group provides the dissociated carbon atom and the NO2 group accepts the H atoms from either the CH3 group or the benzene ring before carbon exits the molecular system. For the second and third carbon dissociation of 2-NT, the energy barriers are 6.70 eV and 7.43 eV, respectively, and two 226 nm photons would need to be absorbed by the molecule. If extra NO is present during the first carbon dissociation of 2-NT, it gets involved in the last two decomposition steps and forms a C=NH-N=O structure which stabilizes the decomposition products and lowers the energy barrier from 5.22 eV to 4.70 eV. However, for the second and third carbon dissociation of 2-NT, the NO molecules have no apparent effect. For nitrotoluene molecules with two or three NO2 groups (i.e., 2,4-DNT, 2,6-DNT, 3,4-DNT, and 2,4,6-TNT), the first carbon dissociation energies are between 5.26 eV and 5.57 eV. The carbon dissociation pathways for these molecules are similar to those of 2-NT. In 2,4-DNT, the lowest energy barriers for the second and third carbon dissociation are 6.54 eV and 6.60 eV, respectively, which are about 1 eV higher than the energy barrier for the first carbon dissociation. In case of 2,4-DNT/NO and 2,4,6-TNT/NO, NO acts as a catalyst in the first carbon dissociation processes and forms a C=NH-N=O structure which lowers the energy barriers by 0.48 eV and 0

  19. Electron correlation in molecules

    CERN Document Server

    Wilson, S

    2007-01-01

    Electron correlation effects are of vital significance to the calculation of potential energy curves and surfaces, the study of molecular excitation processes, and in the theory of electron-molecule scattering. This text describes methods for addressing one of theoretical chemistry's central problems, the study of electron correlation effects in molecules.Although the energy associated with electron correlation is a small fraction of the total energy of an atom or molecule, it is of the same order of magnitude as most energies of chemical interest. If the solution of quantum mechanical equatio

  20. Study of inner-shell excitation processes from N(1s) orbitals in N2O molecules by electron impact

    International Nuclear Information System (INIS)

    Michelin, S E; Arretche, F; Mazon, K T; Piacentini, J J; Marin, A; Oliveira, H L; Travessini, D; Lee, M-T; Iga, I; Fujimoto, M M

    2007-01-01

    A combination of the iterative Schwinger variational method with the distorted-wave approximation is applied to study excitations of a core-level electron in a triatomic molecule by electron impact. More specifically, we report calculated differential and integral cross sections for the X 1 Σ + → 1,3 Π(2σ → 3π) and X 1 Σ + → 1,3 Π(3σ → 3π) transitions in N 2 O in the 415-900 eV incident energy range. The RI(1:3) ratios, obtained via dividing the distorted-wave integral cross sections for transitions leading to the singlet core-excited states by those leading to triplet states, are also reported. The generalized oscillator-strength profiles for the singlet transitions have also been calculated at the incident energy of 3400 eV. The comparison of these quantities with the available theoretical and experimental data reported in the literature is encouraging

  1. Cross-section and rate coefficient calculation for electron impact excitation, ionisation and dissociation of H2 and OH molecules

    International Nuclear Information System (INIS)

    Riahi, R.; Ben Lakhdar, Z.; Teulet, Ph.; Gleizes, A.

    2006-01-01

    The weighted total cross-sections (WTCS) theory is used to calculate electron impact excitation, ionization and dissociation cross-sections and rate coefficients of OH, H 2 , OH + , H 2 + , OH - and H 2 - diatomic molecules in the temperature range 1500-15000 K. Calculations are performed for H 2 (X, B, C), OH(X, A, B), H 2 + (X), OH + (X, a, A, b, c), H 2 - (X) and OH - (X) electronic states for which Dunham coefficients are available. Rate coefficients are calculated from WTCS assuming Maxwellian energy distribution functions for electrons and heavy particles. One and 2 temperatures (θ e and θ g respectively for electron and heavy particles kinetic temperatures) results are presented and fitting parameters (a, b and c) are given for each reaction rate coefficient: k(θ) a(θ b )exp(-c/θ). (authors)

  2. Ab Initio Model for Vibrational Excitation of Polar Molecules by Low-Energy Electrons

    Science.gov (United States)

    Vanroose, W. I.; Rescigno, T. N.; McCurdy, C. W.

    2003-05-01

    Vibrational excitation of the hydrogen halides by electron impact has been a subject of continued interest ever since the first observations of pronounced threshold peaks in the cross sections by Rohr and Linder twenty five years ago. Two semi-empirical models have been developed to explain these features, one a virtual state model by Gauyacq and Herzenberg based on effective-range theory, the other by Domcke and co-workers based on a non-local Feshbach resonance model. We will show that a non-empirical model can be formulated which captures the essential features of the observed cross sections. The only parameters needed to implement the calculations are the potential energy curve of the negative ion in the region where it is bound, the potential curve of the neutral target and its R-dependent dipole moment. We use an effective range theory for the nuclear dynamics, which can be implemented without an expansion in target vibrational states, instead of non-local equations derived from Feshbach partitioning. Another new element is the use of a dipole coupled partial-wave model to predict the analytic continuation of the negative ion potential curve into the continuum. We will illustrate the new model with results for electron-HCl scattering.

  3. Electron capture and excitation in collisions of O+(4S,2D,2P) with H2 molecules

    International Nuclear Information System (INIS)

    Pichl, Lukas; Li Yan; Liebermann, Heinz-Peter; Buenker, Robert J.; Kimura, Mineo

    2004-01-01

    Using an electronic-state close-coupling method, we treated the electron capture and excitation processes of O + ions both in ground state O + ( 4 S) and metastable states O +* ( 2 D) and O +* ( 2 P) in collisions with the H 2 molecule. In the ground-state projectile energy region considered (from 50 eV/amu to 10 keV/amu), the experimental data vary by orders of magnitude: our results smoothly connect to the data by Flesch and Ng [J. Chem. Phys. 94, 2372 (1991)] and Xu et al. [J. Phys. B 23, 1235 (1990)] at low energy and agree with Phaneuf et al. [Phys. Rev. A 17, 534 (1978)] in the high-energy region. The present values differ from Sieglaff et al. [Phys. Rev. A 59, 3538 (1999)] and Nutt et al. [J. Phys. B 12, L157 (1979)], especially in the energy region below 1 keV/amu. We provide the first calculated state-resolved cross sections of electron capture and target-projectile electronic excitations for the O + ( 4 S, 2 D, 2 P)-H 2 collision system

  4. Cross-sections for dissociative excitation of lead atom in collisions of slow electrons with PbI2 molecules

    International Nuclear Information System (INIS)

    Smirnov, Yu.M.

    2006-01-01

    The dissociative excitation of the lead atom in e-PbI 2 collisions has been studied experimentally. 27 excitation cross-sections are measured at an exciting-electron energy of 100 eV. Nine optical excitation functions are recorded at the electron energy varying in the 0-100 eV range. The most possible reaction channels at low electron energies along with the relation of the dissociative-excitation cross-sections of the lead atom both in e-PbI 2 and e-PbCl 2 collisions are discussed. (authors)

  5. Dissociative electron attachment to vibrationally excited H{sub 2} molecules involving the {sup 2}{Sigma}{sub g}{sup +} resonant Rydberg electronic state

    Energy Technology Data Exchange (ETDEWEB)

    Celiberto, R., E-mail: r.celiberto@poliba.it [Department of Water Engineering and Chemistry, Polytechnic of Bari, 70125 Bari (Italy); Institute of Inorganic Methodologies and Plasmas, CNR, 70125 Bari (Italy); Janev, R.K., E-mail: r.janev@fz-juelich.de [Macedonian Academy of Sciences and Arts, P.O.B 428, 1000 Skopje (Macedonia, The Former Yugoslav Republic of); Institute of Energy and Climate Research - Plasma Physics, Forschungszentrum Juelich GmbH Association EURATOM-FZJ, Partner in Trilateral Euregio Cluster, 52425 Juelich (Germany); Wadehra, J.M., E-mail: wadehra@wayne.edu [Physics Department, Wayne State University, Detroit, MI 48202 (United States); Tennyson, J., E-mail: j.tennyson@ucl.ac.uk [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

    2012-04-04

    Graphical abstract: Dissociative electron attachment cross sections as a function of the incident electron energy and for the initial vibration levels v{sub i} = 0-5, 10 of the H{sub 2} molecule. Highlights: Black-Right-Pointing-Pointer We calculated electron-hydrogen dissociative attachment cross sections and rates coefficients. Black-Right-Pointing-Pointer Collision processes occurring through a resonant Rydberg state are considered. Black-Right-Pointing-Pointer Cross sections and rates were obtained for vibrationally excited hydrogen molecules. Black-Right-Pointing-Pointer The cross sections exhibit pronounced oscillatory structures. Black-Right-Pointing-Pointer A comparison with the process involving the electron-hydrogen resonant ground state is discussed. - Abstract: Dissociative electron attachment cross sections (DEA) on vibrationally excited H{sub 2} molecule taking place via the {sup 2}{Sigma}{sub g}{sup +} Rydberg-excited resonant state are studied using the local complex potential (LCP) model for resonant collisions. The cross sections are calculated for all initial vibrational levels (v{sub i} = 0-14) of the neutral molecule. In contrast to the previously noted dramatic increase in the DEA cross sections with increasing v{sub i}, when the process proceeds via the X {sup 2}{Sigma}{sub u}{sup +} shape resonance of H{sub 2}, for the {sup 2}{Sigma}{sub g}{sup +} Rydberg resonance the cross sections increase only gradually up to v{sub i} = 3 and then decrease. Moreover, the cross sections for v{sub i} Greater-Than-Or-Slanted-Equal-To 6 exhibit pronounced oscillatory structures. A discussion of the origin of the observed behavior of calculated cross sections is given. The DEA rate coefficients for all v{sub i} levels are also calculated in the 0.5-1000 eV temperature range.

  6. Rate coefficients for dissociative attachment and resonant electron-impact dissociation involving vibrationally excited O{sub 2} molecules

    Energy Technology Data Exchange (ETDEWEB)

    Laporta, V. [Istituto di Metodologie Inorganiche e dei Plasmi, CNR, Bari, Italy and Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom); Celiberto, R. [Dipartimento di Ingegneria Civile, Ambientale, del Territorio, Edile e di Chimica, Politecnico di Bari, Italy and Istituto di Metodologie Inorganiche e dei Plasmi, CNR, Bari (Italy); Tennyson, J. [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

    2014-12-09

    Rate coefficients for dissociative electron attachment and electron-impact dissociation processes, involving vibrationally excited molecular oxygen, are presented. Analytical fits of the calculated numerical data, useful in the applications, are also provided.

  7. Ab initio calculations of dissociative excitation of water and methane molecules upon electron impact at low energies

    International Nuclear Information System (INIS)

    Gil, T.J.; McCurdy, C.W.; Rescigno, T.N.; Lengsfield, B.H. III

    1994-01-01

    The authors are reporting results of ab-initio calculations of electron-impact excitation of water and methane occurring at scattering energies up to 60 eV. The authors consider dissociative excited states of both systems since the understanding of their chemistry has considerable importance in plasma technology and atmospheric research. In the case of methane the authors are dealing with the promotion of a valence electron into Rydberg orbitals, while in water the excited states have one electron in an antibonding unoccupied valence orbital and support Feshbach resonances. The authors discuss issues related to convergence of the close-coupling expansion in the case of Rydberg excitation, where the authors have coupled up to 16 channels. The practical realization of the calculation within the framework of the complex Kohn variational principle represents merging of quantum chemistry and quantum scattering theory and is also discussed

  8. The photodissociation and reaction dynamics of vibrationally excited molecules

    Energy Technology Data Exchange (ETDEWEB)

    Crim, F.F. [Univ. of Wisconsin, Madison (United States)

    1993-12-01

    This research determines the nature of highly vibrationally excited molecules, their unimolecular reactions, and their photodissociation dynamics. The goal is to characterize vibrationally excited molecules and to exploit that understanding to discover and control their chemical pathways. Most recently the author has used a combination of vibrational overtone excitation and laser induced fluorescence both to characterize vibrationally excited molecules and to study their photodissociation dynamics. The author has also begun laser induced grating spectroscopy experiments designed to obtain the electronic absorption spectra of highly vibrationally excited molecules.

  9. Assessment of oscillator strengths with multiconfigurational short-range density functional theory for electronic excitations in organic molecules

    DEFF Research Database (Denmark)

    Hedegård, Erik Donovan

    2017-01-01

    We have in a series of recent papers investigated electronic excited states with a hybrid between a complete active space self-consistent field (CASSCF) wave function and density functional theory (DFT). This method has been dubbed the CAS short-range DFT method (CAS–srDFT). The previous papers...

  10. Isotope separation using vibrationally excited molecules

    International Nuclear Information System (INIS)

    Woodroffe, J.A.; Keck, J.C.

    1979-01-01

    Vibrational excitation of molecules having components of a selected isotope type is used to produce a conversion from vibrational to translational excitation of the molecules by collision with the molecules of a heavy carrier gas. The resulting difference in translaton between the molecules of the selected isotope type and all other molecules of the same compound permits their separate collection. When applied to uranium enrichment, a subsonic cryogenic flow of molecules of uranium hexafluoride in combination with an argon carrier gas is directed through a cooled chamber that is illuminated by laser radiaton tuned to vibrationally excite the uranium hexafluoride molecules of a specific uranium isotope. The excited molecules collide with carrier gas molecules, causing a conversion of the excitation energy into a translation of the excited molecule, which results in a higher thermal energy or diffusivity than that of the other uranium hexafluoride molecules. The flowing molecules including the excited molecules directly enter a set of cryogenically cooled channels. The higher thermal velocity of the excited molecules increases the probability of their striking a collector surface. The molecules which strike this surface immediately condense. After a predetermined thickness of molecules is collected on the surface, the flow of uranium hexafluoride is interrupted and the chamber heated to the point of vaporization of the collected hexafluoride, permitting its removal. (LL)

  11. Sub-500 fs electronically nonadiabatic chemical dynamics of energetic molecules from the S1 excited state: Ab initio multiple spawning study.

    Science.gov (United States)

    Ghosh, Jayanta; Gajapathy, Harshad; Konar, Arindam; Narasimhaiah, Gowrav M; Bhattacharya, Atanu

    2017-11-28

    Energetic materials store a large amount of chemical energy. Different ignition processes, including laser ignition and shock or compression wave, initiate the energy release process by first promoting energetic molecules to the electronically excited states. This is why a full understanding of initial steps of the chemical dynamics of energetic molecules from the excited electronic states is highly desirable. In general, conical intersection (CI), which is the crossing point of multidimensional electronic potential energy surfaces, is well established as a controlling factor in the initial steps of chemical dynamics of energetic molecules following their electronic excitations. In this article, we have presented different aspects of the ultrafast unimolecular relaxation dynamics of energetic molecules through CIs. For this task, we have employed ab initio multiple spawning (AIMS) simulation using the complete active space self-consistent field (CASSCF) electronic wavefunction and frozen Gaussian-based nuclear wavefunction. The AIMS simulation results collectively reveal that the ultrafast relaxation step of the best energetic molecules (which are known to exhibit very good detonation properties) is completed in less than 500 fs. Many, however, exhibit sub-50 fs dynamics. For example, nitro-containing molecules (including C-NO 2 , N-NO 2 , and O-NO 2 active moieties) relax back to the ground state in approximately 40 fs through similar (S 1 /S 0 ) CI conical intersections. The N 3 -based energetic molecule undergoes the N 2 elimination process in 40 fs through the (S 1 /S 0 ) CI conical intersection. Nitramine-Fe complexes exhibit sub-50 fs Fe-O and N-O bond dissociation through the respective (S 1 /S 0 ) CI conical intersection. On the other hand, tetrazine-N-oxides, which are known to exhibit better detonation properties than tetrazines, undergo internal conversion in a 400-fs time scale, while the relaxation time of tetrazine is very long (about 100 ns). Many

  12. Sub-500 fs electronically nonadiabatic chemical dynamics of energetic molecules from the S1 excited state: Ab initio multiple spawning study

    Science.gov (United States)

    Ghosh, Jayanta; Gajapathy, Harshad; Konar, Arindam; Narasimhaiah, Gowrav M.; Bhattacharya, Atanu

    2017-11-01

    Energetic materials store a large amount of chemical energy. Different ignition processes, including laser ignition and shock or compression wave, initiate the energy release process by first promoting energetic molecules to the electronically excited states. This is why a full understanding of initial steps of the chemical dynamics of energetic molecules from the excited electronic states is highly desirable. In general, conical intersection (CI), which is the crossing point of multidimensional electronic potential energy surfaces, is well established as a controlling factor in the initial steps of chemical dynamics of energetic molecules following their electronic excitations. In this article, we have presented different aspects of the ultrafast unimolecular relaxation dynamics of energetic molecules through CIs. For this task, we have employed ab initio multiple spawning (AIMS) simulation using the complete active space self-consistent field (CASSCF) electronic wavefunction and frozen Gaussian-based nuclear wavefunction. The AIMS simulation results collectively reveal that the ultrafast relaxation step of the best energetic molecules (which are known to exhibit very good detonation properties) is completed in less than 500 fs. Many, however, exhibit sub-50 fs dynamics. For example, nitro-containing molecules (including C-NO2, N-NO2, and O-NO2 active moieties) relax back to the ground state in approximately 40 fs through similar (S1/S0)CI conical intersections. The N3-based energetic molecule undergoes the N2 elimination process in 40 fs through the (S1/S0)CI conical intersection. Nitramine-Fe complexes exhibit sub-50 fs Fe-O and N-O bond dissociation through the respective (S1/S0)CI conical intersection. On the other hand, tetrazine-N-oxides, which are known to exhibit better detonation properties than tetrazines, undergo internal conversion in a 400-fs time scale, while the relaxation time of tetrazine is very long (about 100 ns). Many other characteristics of

  13. Excitation energy transfer from dye molecules to doped graphene

    Indian Academy of Sciences (India)

    Recently, we have reported theoretical studies on the rate of energy transfer from an electronically excited molecule to graphene. It was found that graphene is a very efficient quencher of the electronically excited states and that the rate -4. The process was found to be effective up to 30 which is well beyond the ...

  14. Angle-resolving time-of-flight electron spectrometer for near-threshold precision measurements of differential cross sections of electron-impact excitation of atoms and molecules

    International Nuclear Information System (INIS)

    Lange, M.; Matsumoto, J.; Setiawan, A.; Panajotovic, R.; Harrison, J.; Lower, J. C. A.; Newman, D. S.; Mondal, S.; Buckman, S. J.

    2008-01-01

    This article presents a new type of low-energy crossed-beam electron spectrometer for measuring angular differential cross sections of electron-impact excitation of atomic and molecular targets. Designed for investigations at energies close to excitation thresholds, the spectrometer combines a pulsed electron beam with the time-of-flight technique to distinguish between scattering channels. A large-area, position-sensitive detector is used to offset the low average scattering rate resulting from the pulsing duty cycle, without sacrificing angular resolution. A total energy resolution better than 150 meV (full width at half maximum) at scattered energies of 0.5-3 eV is achieved by monochromating the electron beam prior to pulsing it. The results of a precision measurement of the differential cross section for electron-impact excitation of helium, at an energy of 22 eV, are used to assess the sensitivity and resolution of the spectrometer

  15. Electrons in Molecules

    Indian Academy of Sciences (India)

    “What are electrons doing in molecules?” This is a deceptively simple question that scientists have been trying to answer for more than eighty years. With the advent of quantum mechanics in 1926, it became clear that we must understand the dynamics of electronic motion in atoms, molecules and solids in order to explain ...

  16. Quantum analysis in the transition process to excited state of an oxygen molecule induced by electron collisions; Denshi shototsu ni tomonau sanso bunshi ni okeru reiki jotai sen`i no ryoshironteki kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Ishimaru, K. [Gifu National College of Technology, Gifu (Japan); Okazaki, K. [Tokyo Inst. of Technology, Tokyo (Japan)

    1996-06-25

    For understanding of fundamental chemical reactions under a highly non equilibrium condition which is quite often used in plasma processing, the relevant atomic and molecular processes must be clarified. In this study, an analysis of the transition process to the excited state of an oxygen molecule induced by electron collisions in the oxygen plasma has been carried out. First, the electron density distribution in an oxygen molecule has been calculated using the extended Huckel molecular orbital method. Then, the electron potential energy distribution in the transition process to the excited state has been estimated. The electron behavior has been calculated using the estimated unidimensional electron potential energy distribution and unsteady quantum mechanics. As a result, the transition process to the excited state of an oxygen molecule induced by electron collisions and its conditions have been clarified qualitatively. 9 refs., 9 figs.

  17. Spectroscopy and reactions of vibrationally excited transient molecules

    Energy Technology Data Exchange (ETDEWEB)

    Dai, H.L. [Univ. of Pennsylvania, Philadelphia (United States)

    1993-12-01

    Spectroscopy, energy transfer and reactions of vibrationally excited transient molecules are studied through a combination of laser-based excitation techniques and efficient detection of emission from the energized molecules with frequency and time resolution. Specifically, a Time-resolved Fourier Transform Emission Spectroscopy technique has been developed for detecting dispersed laser-induced fluorescence in the IR, visible and UV regions. The structure and spectroscopy of the excited vibrational levels in the electronic ground state, as well as energy relaxation and reactions induced by specific vibronic excitations of a transient molecule can be characterized from time-resolved dispersed fluorescence in the visible and UV region. IR emissions from highly vibrational excited levels, on the other hand, reveal the pathways and rates of collision induced vibrational energy transfer.

  18. Isotope separation using vibrationally excited molecules

    International Nuclear Information System (INIS)

    Woodroffe, J.A.; Keck, J.C.

    1977-01-01

    A system for isotope separation or enrichment wherein molecules of a selected isotope type in a flow of molecules of plural isotope types are vibrationally excited and collided with a background gas to provide enhanced diffusivity for the molecules of the selected isotope type permitting their separate collection. The system typically is for the enrichment of uranium using a uranium hexafluoride gas in combination with a noble gas such as argon. The uranium hexafluoride molecules having a specific isotope of uranium are vibrationally excited by laser radiation. The vibrational energy is converted to a translation energy upon collision with a particle of the background gas and the added translation energy enhances the diffusivity of the selected hexafluoride molecules facilitating its condensation on collection surfaces provided for that purpose. This process is periodically interrupted and the cryogenic flow halted to permit evaporation of the collected molecules to provide a distinct, enriched flow

  19. Electron-molecule collisions

    CERN Document Server

    Takayanagi, Kazuo

    1984-01-01

    Scattering phenomena play an important role in modern physics. Many significant discoveries have been made through collision experiments. Amongst diverse kinds of collision systems, this book sheds light on the collision of an electron with a molecule. The electron-molecule collision provides a basic scattering problem. It is scattering by a nonspherical, multicentered composite particle with its centers having degrees of freedom of motion. The molecule can even disintegrate, Le., dissociate or ionize into fragments, some or all of which may also be molecules. Although it is a difficult problem, the recent theoretical, experimental, and computational progress has been so significant as to warrant publication of a book that specializes in this field. The progress owes partly to technical develop­ ments in measurements and computations. No less important has been the great and continuing stimulus from such fields of application as astrophysics, the physics of the earth's upper atmosphere, laser physics, radiat...

  20. Electron Accumulative Molecules.

    Science.gov (United States)

    Buades, Ana B; Sanchez Arderiu, Víctor; Olid-Britos, David; Viñas, Clara; Sillanpää, Reijo; Haukka, Matti; Fontrodona, Xavier; Paradinas, Markos; Ocal, Carmen; Teixidor, Francesc

    2018-02-28

    With the goal to produce molecules with high electron accepting capacity and low reorganization energy upon gaining one or more electrons, a synthesis procedure leading to the formation of a B-N(aromatic) bond in a cluster has been developed. The research was focused on the development of a molecular structure able to accept and release a specific number of electrons without decomposing or change in its structural arrangement. The synthetic procedure consists of a parallel decomposition reaction to generate a reactive electrophile and a synthesis reaction to generate the B-N(aromatic) bond. This procedure has paved the way to produce the metallacarboranylviologen [M(C 2 B 9 H 11 )(C 2 B 9 H 10 )-NC 5 H 4 -C 5 H 4 N-M'(C 2 B 9 H 11 )(C 2 B 9 H 10 )] (M = M' = Co, Fe and M = Co and M' = Fe) and semi(metallacarboranyl)viologen [3,3'-M(8-(NC 5 H 4 -C 5 H 4 N-1,2-C 2 B 9 H 10 )(1',2'-C 2 B 9 H 11 )] (M = Co, Fe) electron cumulative molecules. These molecules are able to accept up to five electrons and to donate one in single electron steps at accessible potentials and in a reversible way. By targeted synthesis and corresponding electrochemical tests each electron transfer (ET) step has been assigned to specific fragments of the molecules. The molecules have been carefully characterized, and the electronic communication between both metal centers (when this situation applies) has been definitely observed through the coplanarity of both pyridine fragments. The structural characteristics of these molecules imply a low reorganization energy that is a necessary requirement for low energy ET processes. This makes them electronically comparable to fullerenes, but on their side, they have a wide range of possible solvents. The ET from one molecule to another has been clearly demonstrated as well as their self-organizing capacity. We consider that these molecules, thanks to their easy synthesis, ET, self-organizing capacity, wide range of solubility, and easy processability, can

  1. Chemical sputtering by impact of excited molecules

    International Nuclear Information System (INIS)

    Krstic, P.S.; Reinhold, C.O.; Stuart, S.J.

    2007-01-01

    We study chemical sputtering of deuterated amorphous carbon surfaces by D atoms, vibrationally excited D 2 , and dissociating D 3 molecules, in a range of impact energies, 7.5 - 30 eV/D. We analyze the role of the internal state, i.e. the vibrationally excited and dissociating states of the neutral molecules resulting from above-surface neutralization of impacting molecular ions in typical sputtering experiments. The sputtering yields are shown to considerably increase with the internal vibrational energy at the lowest impact energies. By comparison of calculated and measured yields we draw conclusions regarding the possible mechanisms for neutralization. (authors)

  2. Theoretical study of intermolecular energy transfer involving electronically excited molecules: He(1S) + H2(B 1Σ/sub u/+)

    International Nuclear Information System (INIS)

    Grimes, R.M.

    1986-11-01

    To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H 2 (B 1 Σ/sub u/ + ) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H 2 (B 1 Σ/sub u/ + ). The potential energy surface (PES) is highly anisotropic and has a van der Waals well of about 0.03 eV for C/sub 2v/ approach. Avoided PES crossings occur with He + H 2 (E,F 1 Σ/sub g/ + ) and with He + H 2 (X 1 Σ/sub g/ + ) and cause a local maximum and a deep minimum in the He + H 2 (B 1 Σ/sub u/ + ) PES, respectively. The crossing with He + H 2 (X 1 Σ/sub g/ + ) provides a mechanism for fluorescence quenching. The computed CI energies were combined with previous multi-reference double excitation CI calculations and fit with analytic functions for convenience in scattering calculations. Accurate dipole polarizabilities and quadrupole moment of H 2 (B 1 Σ/sub u/ + ) were computed for use in the multipole expansion, which is the analytic form of the long-range PES. 129 refs., 28 figs., 35 tabs

  3. Studies of interstellar vibrationally-excited molecules

    International Nuclear Information System (INIS)

    Ziurys, L.M.; Snell, R.L.; Erickson, N.R.

    1986-01-01

    Several molecules thus far have been detected in the ISM in vibrationally-excited states, including H 2 , SiO, HC 3 N, and CH 3 CN. In order for vibrational-excitation to occur, these species must be present in unusually hot and dense gas and/or where strong infrared radiation is present. In order to do a more thorough investigation of vibrational excitation in the interstellar medium (ISM), studies were done of several mm-wave transitions originating in excited vibrational modes of HCN, an abundant interstellar molecule. Vibrationally-excited HCN was recently detected toward Orion-KL and IRC+10216, using a 12 meter antenna. The J=3-2 rotational transitions were detected in the molecule's lowest vibrational state, the bending mode, which is split into two separate levels, due to l-type doubling. This bending mode lies 1025K above ground state, with an Einstein A coefficient of 3.6/s. The J=3-2 line mode of HCN, which lies 2050K above ground state, was also observed toward IRC+10216, and subsequently in Orion-KL. Further measurements of vibrationally-excited HCN were done using a 14 meter telescope, which include the observations of the (0,1,0) and (0,2,0) modes towards Orion-KL, via their J=3-2 transitions at 265-267 GHz. The spectrum of the J=3-2 line in Orion taken with the 14 meter telescope, is shown, along with a map, which indicates that emission from vibrationally-excited HCN arises from a region probably smaller than the 14 meter telescope's 20 arcsec beam

  4. Mean excitation energy for molecules of hydrogen and carbon

    Science.gov (United States)

    Wilson, J. W.; Kamaratos, E.

    1981-01-01

    The Gordon-Kim electron gas model of molecular bonding is used to calculate correction factors for the Bragg rule for molecules of hydrogen and carbon. General rules for molecular mean excitation energies are obtained that agree to about 4% with experimental values.

  5. Stereodirectional images of molecules oriented by a variable-voltage hexapolar field: Fragmentation channels of 2-bromobutane electronically excited at two photolysis wavelengths

    Science.gov (United States)

    Nakamura, Masaaki; Yang, Shiun-Jr; Lin, King-Chuen; Kasai, Toshio; Che, Dock-Chil; Lombardi, Andrea; Palazzetti, Federico; Aquilanti, Vincenzo

    2017-07-01

    The asymmetric-top molecule 2-bromobutane is oriented by means of a hexapole state selector; the angular distribution of the bromine atom photofragment, for the two fine-structure components, is acquired by velocity-map ion imaging. The molecular beam, spatially oriented along the time-of-flight axis, is intersected with a linearly polarized laser, whose polarization is tilted by 45° with respect to the detector surface. To obtain the mixing ratio of the perpendicular and parallel transitions, the fragment ion images and angular distributions can be appropriately simulated to give insight on the population mechanism of the specific electronic state involved at each selected excitation wavelength. The photofragment images obtained at 238.6 nm yielded an asymmetry factor β1 of 0.67, indicative of the extent of molecular orientation, and an anisotropy parameter β2 of 1.03, which is a signature of a prevailing parallel transition along the C-Br axis. When the photolysis wavelength is tuned to 254.1 nm, the corresponding angular distribution is less asymmetric (β1 = 0.24) and the obtained small value β2 = 0.12 is a characteristic of a predominantly perpendicular transition. The photofragment angular distributions are also affected by hexapole voltage, especially regarding the asymmetry factor, and this aspect provides information on the effect of molecular orientation.

  6. S1←S0 vibronic spectra and structure of cyclopropanecarboxaldehyde molecule in the S1 lowest excited singlet electronic state

    International Nuclear Information System (INIS)

    Godunov, I.A.; Yakovlev, N.N.; Terentiev, R.V.; Maslov, D.V.; Bataev, V.A.; Abramenkov, A.V.

    2016-01-01

    The S 1 ←S 0 vibronic spectra of gas-phase absorption at room temperature and fluorescence excitation of jet-cooled cyclopropanecarboxaldehyde (CPCA, c-C 3 H 5 CHO)were obtained and analyzed. In addition, the quantum chemical calculation (CASPT2/cc-pVTZ)was carried out for CPCA in the ground (S 0 ) and lowest excited singlet (S 1 ) electronic states. As a result, it was proved that the S 1 ←S 0 electronic excitation of the CPCA conformers (syn and anti) causes (after geometrical relaxation) significant structural changes, namely, the carbonyl fragments become non-planar and the cyclopropyl groups rotate around the central C–C bond. As a consequence, the potential energy surface of CPCA in the S 1 state has six minima, 1ab, 2ab, and 3ab, corresponding to three pairs of mirror symmetry conformers: a and b. It was shown that vibronic bands of experimental spectra can be assigned to the 2(S 1 )←syn(S 0 ) electronic transition with the origin at 30,481 cm −1 . A number of fundamental vibrational frequencies for the 2 conformer of CPCA were assigned. In addition, several inversional energy levels for the 2 conformer were found and the 2a↔2b potential function of inversion was determined. The experimental barrier to inversion and the equilibrium angle between the CH bond and the CCO plane were calculated as 570 cm −1 and 28°, respectively. - Highlights: • S 1 ←S 0 vibronic gas-phase absorption spectrum of cyclopropanecarboxaldehyde (CPCA). • S 1 ←S 0 fluorescence excitation spectrum of CPCA. • Ab initio calculation for CPCA in S 0 and S 1 electronic states. • Structural changes of the CPCA at S 1 ←S 0 electronic excitation.

  7. Radiation produced by electrons incident on molecules

    International Nuclear Information System (INIS)

    Moehlman, G.R.

    1977-01-01

    The work described in this thesis deals with light intensity measurements of emission spectra (1850-9000 A) produced by a continuous or pulsed beam of monoenergetic electrons (0 - 2000 eV) incident on a variety of molecular gases like H 2 , D 2 , H 2 O, HCl, NH 3 and several hydrocarbons. The emission spectra are dominated by fluorescence from excited fragments produced via dissociative excitation, besides fluorescence from excited parent molecules themselves. The experimental results thus obtained are expressed in terms of emission cross sections and lifetimes

  8. THE ELECTRONIC-STRUCTURE OF THE PTH MOLECULE - FULLY RELATIVISTIC CONFIGURATION-INTERACTION CALCULATIONS OF THE GROUND AND EXCITED-STATES

    NARCIS (Netherlands)

    VISSCHER, L; SAUE, T; NIEUWPOORT, WC; FAEGRI, K; GROPEN, O

    1993-01-01

    Fully relativistic all-electron self-consistent field calculations based on the Dirac-Coulomb Hamiltonian have been performed on the three lowest lying states of the PtH molecule. The resulting four-component Dirac-Hartree-Fock (DHF) molecular spinors are subsequently used in relativistic

  9. Excitation of lowest electronic states of thymine by slow electrons

    Science.gov (United States)

    Chernyshova, I. V.; Kontros, E. J.; Markush, P. P.; Shpenik, O. B.

    2013-11-01

    Excitation of lowest electronic states of the thymine molecules in the gas phase is studied by elec- tron energy loss spectroscopy. In addition to dipole-allowed transitions to singlet states, transitions to the lowest triplet states were observed. The low-energy features of the spectrum at 3.66 and 4.61 eV are identified with the excitation of the first triplet states 13 A' (π → π*) and 13 A″ ( n → π*). The higher-lying features at 4.96, 5.75, 6.17, and 7.35 eV are assigned mainly to the excitation of the π → π* transitions to the singlet states of the molecule. The excitation dynamics of the lowest states is studied. It is found that the first triplet state 13 A'(π → π*) is most efficiently excited at a residual energy close to zero, while the singlet 21 A'(π → π*) state is excited with almost identical efficiency at different residual energies.

  10. Electron affinities of atoms, molecules, and radicals

    International Nuclear Information System (INIS)

    Christodoulides, A.A.; McCorkle, D.L.; Christophorou, L.G.

    1982-01-01

    We review briefly but comprehensively the theoretical, semiempirical and experimental methods employed to determine electron affinities (EAs) of atoms, molecules and radicals, and summarize the EA data obtained by these methods. The detailed processes underlying the principles of the experimental methods are discussed very briefly. It is, nonetheless, instructive to recapitulate the definition of EA and those of the related quantities, namely, the vertical detachment energy, VDE, and the vertical attachment energy, VAE. The EA of an atom is defined as the difference in total energy between the ground state of the neutral atom (plus the electron at rest at infinity) and its negative ion. The EA of a molecule is defined as the difference in energy between the neutral molecule plus an electron at rest at infinity and the molecular negative ion when both, the neutral molecules and the negative ion, are in their ground electronic, vibrational and rotational states. The VDE is defined as the minimum energy required to eject the electron from the negative ion (in its ground electronic and nuclear state) without changing the internuclear separation; since the vertical transition may leave the neutral molecule in an excited vibrational/rotational state, the VDE, although the same as the EA for atoms is, in general, different (larger than), from the EA for molecules. Similarly, the VAE is defined as the difference in energy between the neutral molecule in its ground electronic, vibrational and rotational states plus an electron at rest at infinity and the molecular negative ion formed by addition of an electron to the neutral molecule without allowing a change in the intermolecular separation of the constituent nuclei; it is a quantity appropriate to those cases where the lowest negative ion state lies above the ground states of the neutral species and is less or equal to EA

  11. Application of R-matrix theory to resonant reactive electron-molecule scattering: Vibrational excitation and dissociative attachment of N2 and F2

    International Nuclear Information System (INIS)

    Wong, C.F.; Light, J.C.

    1984-01-01

    Based on the R-matrix approach of Schneider et al. [J. Phys. B 12, L 365 (1979)] to reactive electron-molecule scattering, a new propagative R-matrix method (PRMM) is presented which is more appropriate for polyatomic systems. The new method should be useful in other calculations where complicated integrals need to be propagated. We also introduce an effective R-matrix model (ERMM) in which the usual resonance parameters (potential and width) can be used as input in model R-matrix calculations. The PRMM and ERMM have been applied to the electron-N 2 system and the electron-F 2 system. The results agree very well with previous calculations for both vibrationally inelastic scattering and dissociative attachment when identical potentials and parameters are used

  12. Isotope separation using vibrationally excited molecules

    International Nuclear Information System (INIS)

    1979-01-01

    This invention relates to isotope separation employing isotopically selective vibrational excitation and vibration-translation reactions of the excited particles. Uranium enrichment, using uranium hexafluoride, is a particular embodiment. (U.K.)

  13. Electron Scattering From Atoms, Molecules, Nuclei, and Bulk Matter

    CERN Document Server

    Whelan, Colm T

    2005-01-01

    Topics that are covered include electron scattering in the scanning TEM; basic theory of inelastic electron imaging; study of confined atoms by electron excitation; helium bubbles created in extreme pressure with application to nuclear safety; lithium ion implantation; electron and positron scattering from clusters; electron scattering from physi- and chemi-absorbed molecules on surfaces; coincidence studies; electron scattering from biological molecules; electron spectroscopy as a tool for environmental science; electron scattering in the presence of intense fields; electron scattering from astrophysical molecules; electon interatctions an detection of x-ray radiation.

  14. Inner-shell excitation and ionic fragmentation of molecules

    International Nuclear Information System (INIS)

    Hitchcock, A.P.; Tyliszczak, T.; Cavell, R.G.

    1997-01-01

    Inner-shell excitation and associated decay spectroscopies are site specific probes of electronic and geometrical structure and photoionization dynamics. X-ray absorption probes the geometric and electronic structure, while time-of-flight mass spectrometry with multi-coincidence detection provides information on the photofragmentation dynamics of the initially produced inner-shell state. Auger decay of inner-shell excited and ionised states is an efficient source of multiply charged ions. The charge separation and fragmentation of these species, studied by photoelectron-photoion-photoion coincidence (also called charge separation mass spectrometry) gives insights into bonding and electronic structure. In molecules, the dependence of the fragmentation process on the X-ray energy can reveal cases of site and/or state selective fragmentation. At the ALS the authors have examined the soft X-ray spectroscopy and ionic fragmentation of a number of molecules, including carboranes, silylenes, phosphorus halides, SF 6 and CO 2 . Their work is illustrated using results from the carborane and PF 3 studies

  15. Inner-shell excitation and ionic fragmentation of molecules

    Energy Technology Data Exchange (ETDEWEB)

    Hitchcock, A.P.; Tyliszczak, T. [McMaster Univ., Hamilton, Ontario (Canada); Cavell, R.G. [Univ. of Alberta, Edmonton (Canada)] [and others

    1997-04-01

    Inner-shell excitation and associated decay spectroscopies are site specific probes of electronic and geometrical structure and photoionization dynamics. X-ray absorption probes the geometric and electronic structure, while time-of-flight mass spectrometry with multi-coincidence detection provides information on the photofragmentation dynamics of the initially produced inner-shell state. Auger decay of inner-shell excited and ionised states is an efficient source of multiply charged ions. The charge separation and fragmentation of these species, studied by photoelectron-photoion-photoion coincidence (also called charge separation mass spectrometry) gives insights into bonding and electronic structure. In molecules, the dependence of the fragmentation process on the X-ray energy can reveal cases of site and/or state selective fragmentation. At the ALS the authors have examined the soft X-ray spectroscopy and ionic fragmentation of a number of molecules, including carboranes, silylenes, phosphorus halides, SF{sub 6} and CO{sub 2}. Their work is illustrated using results from the carborane and PF{sub 3} studies.

  16. Single-Molecule Interfacial Electron Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Lu, H. Peter [Bowling Green State Univ., Bowling Green, OH (United States). Dept. of Chemistry and Center for Photochemical Sciences

    2017-11-28

    spectroscopy and electrochemical AFM metal tip scanning microscopy, focusing on understanding the interfacial electron transfer dynamics at specific nanoscale electron transfer sites with high-spatially and temporally resolved topographic-and-spectroscopic characterization at individual molecule basis, characterizing single-molecule rate processes, reaction driving force, and molecule-substrate electronic coupling. One of the most significant characteristics of our new approach is that we are able to interrogate the complex interfacial electron transfer dynamics by actively pin-point energetic manipulation of the surface interaction and electronic couplings, beyond the conventional excitation and observation.

  17. Single Molecule Electronics and Devices

    Science.gov (United States)

    Tsutsui, Makusu; Taniguchi, Masateru

    2012-01-01

    The manufacture of integrated circuits with single-molecule building blocks is a goal of molecular electronics. While research in the past has been limited to bulk experiments on self-assembled monolayers, advances in technology have now enabled us to fabricate single-molecule junctions. This has led to significant progress in understanding electron transport in molecular systems at the single-molecule level and the concomitant emergence of new device concepts. Here, we review recent developments in this field. We summarize the methods currently used to form metal-molecule-metal structures and some single-molecule techniques essential for characterizing molecular junctions such as inelastic electron tunnelling spectroscopy. We then highlight several important achievements, including demonstration of single-molecule diodes, transistors, and switches that make use of electrical, photo, and mechanical stimulation to control the electron transport. We also discuss intriguing issues to be addressed further in the future such as heat and thermoelectric transport in an individual molecule. PMID:22969345

  18. Spectroscopic probes of vibrationally excited molecules at chemically significant energies

    Energy Technology Data Exchange (ETDEWEB)

    Rizzo, T.R. [Univ. of Rochester, NY (United States)

    1993-12-01

    This project involves the application of multiple-resonance spectroscopic techniques for investigating energy transfer and dissociation dynamics of highly vibrationally excited molecules. Two major goals of this work are: (1) to provide information on potential energy surfaces of combustion related molecules at chemically significant energies, and (2) to test theoretical modes of unimolecular dissociation rates critically via quantum-state resolved measurements.

  19. Theory of coherent molecule to surface electron injection: An ...

    Indian Academy of Sciences (India)

    Administrator

    erogeneous electron transfer from a molecule to a semiconductor occurs before full vibrational relaxa- tion of the excited molecule is achieved. 5,6. Accor- dingly, theoretical description of the decay of the initial state has been formulated to include vibra- tional coherence in the transfer process. 4. 2. Analytical model.

  20. Electron attachment to the phthalide molecule

    Science.gov (United States)

    Asfandiarov, N. L.; Pshenichnyuk, S. A.; Vorob'ev, A. S.; Nafikova, E. P.; Lachinov, A. N.; Kraikin, V. A.; Modelli, A.

    2015-05-01

    Phthalide, the simplest chain of conductive polymer thin film, was investigated by means of Electron Transmission Spectroscopy, Negative Ion Mass Spectrometry, and density functional theory quantum chemistry. It has been found that formation of gas-phase long-lived molecular anions of phthalide around 0.7 eV takes place through cleavage of a C-O bond of the pentacyclic ring of the parent molecular anion to give a vibrationally excited (electronically more stable) open-ring molecular anion. The energy of the transition state for ring opening of the parent negative ion is calculated to be 0.65 eV above the neutral ground state of the molecule. The energy (2.64 eV) evaluated for the corresponding transition state in the neutral molecule is much higher, so that the process of electron detachment from the anion must lead to a neutral molecule with its initial pentacyclic structure. The average lifetime of the molecular negative ions formed at an electron energy of 0.75 eV and 80 °C is measured to be about 100 μs. The known switching effect of thin phthalide films could stem from the presence of a similar open/closed transition state also in the polymer.

  1. Atomic excitation and molecular dissociation by low energy electron collisions

    International Nuclear Information System (INIS)

    Weyland, Marvin

    2016-01-01

    In this work, momentum imaging experiments have been conducted for the electron impact excitation of metastable states in noble gases and for dissociative electron attachment (DEA) in polyatomic molecules. For the electron impact excitation study a new experimental technique has been developed which is able to measure the scattering angle distribution of the electrons by detection of the momentum transfer to the atoms. Momentum transfer images have been recorded for helium and neon at fixed electron impact energy close to the excitation threshold and good agreement with current R-matrix theory calculations was found. A new momentum imaging apparatus for negative ions has been built for the purpose of studying DEA in biologically relevant molecules. During this work, DEA was investigated in the molecules ammonia, water, formic acid, furan, pyridine and in two chlorofluorocarbons. Furthermore, the change of DEA resonance energies when molecules form clusters compared to monomers was investigated in ammonia and formic acid. The experimental results of most studied molecules could be compared to recent theoretical calculations and they support further development in the theoretical description of DEA. The new apparatus built in this work also delivered a superior momentum resolution compared to existing setups. This allows the momentum imaging of heavier fragments and fragments with lower kinetic energy.

  2. Atomic excitation and molecular dissociation by low energy electron collisions

    Energy Technology Data Exchange (ETDEWEB)

    Weyland, Marvin

    2016-11-16

    In this work, momentum imaging experiments have been conducted for the electron impact excitation of metastable states in noble gases and for dissociative electron attachment (DEA) in polyatomic molecules. For the electron impact excitation study a new experimental technique has been developed which is able to measure the scattering angle distribution of the electrons by detection of the momentum transfer to the atoms. Momentum transfer images have been recorded for helium and neon at fixed electron impact energy close to the excitation threshold and good agreement with current R-matrix theory calculations was found. A new momentum imaging apparatus for negative ions has been built for the purpose of studying DEA in biologically relevant molecules. During this work, DEA was investigated in the molecules ammonia, water, formic acid, furan, pyridine and in two chlorofluorocarbons. Furthermore, the change of DEA resonance energies when molecules form clusters compared to monomers was investigated in ammonia and formic acid. The experimental results of most studied molecules could be compared to recent theoretical calculations and they support further development in the theoretical description of DEA. The new apparatus built in this work also delivered a superior momentum resolution compared to existing setups. This allows the momentum imaging of heavier fragments and fragments with lower kinetic energy.

  3. Hydrogen Bonding in the Electronic Excited State

    Science.gov (United States)

    Zhao, Guang-Jiu; Han, Ke-Li; DICP1101 Group Team

    2013-03-01

    Here, I will give a talk on our recent advances in electronic excited-state hydrogen-bonding dynamics and the significant role of excited-state hydrogen bonding on internal conversion (IC), electronic spectral shifts (ESS), photoinduced electron transfer (PET), fluorescence quenching (FQ), intramolecular charge transfer (ICT), and metal-to-ligand charge transfer (MLCT). The combination of various spectroscopic experiments with theoretical calculations has led to tremendous progress in excited-state hydrogen-bonding research. We first demonstrated that intermolecular hydrogen bond in excited state can be greatly strengthened or weakened for many chromophores. We have also clarified that intermolecular hydrogen-bond strengthening and weakening correspond to red-shifts and blue-shifts, respectively, in the electronic spectra. Moreover, radiationless deactivations (via IC, PET, ICT, MLCT, and so on) can be dramatically influenced by excited-state hydrogen bonding. GJZ and KLH thank the NSFC (Nos: 20903094 and 20833008) for financial support.

  4. Symmetry characterization of electrons and lattice excitations

    Directory of Open Access Journals (Sweden)

    Schober H.

    2012-03-01

    Full Text Available Symmetry concerns all aspects of a physical system from the electronic orbitals to structural and magnetic excitations. In this article we will try to elaborate the fundamental connection between symmetry and excitations. As excitations are manyfold in physical systems it is impossible to treat them exhaustively. We thus concentrate on the two topics of Bloch electrons and phonons. These two examples are complementary in the sense that Bloch electrons describe single particles in an external periodic potential while phonons exemplify a decoupled system of interacting particles. The way we develop the argument gives as by-product a short account of molecular orbitals and molecular vibrations.

  5. Sequential nonadiabatic excitation of large molecules and ions driven by strong laser fields

    International Nuclear Information System (INIS)

    Markevitch, Alexei N.; Levis, Robert J.; Romanov, Dmitri A.; Smith, Stanley M.; Schlegel, H. Bernhard; Ivanov, Misha Yu.

    2004-01-01

    Electronic processes leading to dissociative ionization of polyatomic molecules in strong laser fields are investigated experimentally, theoretically, and numerically. Using time-of-flight ion mass spectroscopy, we study the dependence of fragmentation on laser intensity for a series of related molecules and report regular trends in this dependence on the size, symmetry, and electronic structure of a molecule. Based on these data, we develop a model of dissociative ionization of polyatomic molecules in intense laser fields. The model is built on three elements: (i) nonadiabatic population transfer from the ground electronic state to the excited-state manifold via a doorway (charge-transfer) transition; (ii) exponential enhancement of this transition by collective dynamic polarization of all electrons, and (iii) sequential energy deposition in both neutral molecules and resulting molecular ions. The sequential nonadiabatic excitation is accelerated by a counterintuitive increase of a large molecule's polarizability following its ionization. The generic theory of sequential nonadiabatic excitation forms a basis for quantitative description of various nonlinear processes in polyatomic molecules and ions in strong laser fields

  6. selective excitation of vibrational modes of polyatomic molecule

    Indian Academy of Sciences (India)

    Abstract. Mode-selective dynamics of triatomic molecule in the electronic ground state under continuous wave laser pulse is investigated for the discrete vibrational bound states. A non-perturbative approach has been used to analyse the vibrational couplings and dynamics of the molecule. Keywords. Polyatomic molecule ...

  7. Resonant inelastic collisions of electrons with diatomic molecules

    International Nuclear Information System (INIS)

    Houfek, Karel

    2012-01-01

    In this contribution we give a review of applications of the nonlocal resonance theory which has been successfully used for treating the nuclear dynamics of low-energy electron collisions with diatomic molecules over several decades. We give examples and brief explanations of various structures observed in the cross sections of vibrational excitation and dissociative electron attachment to diatomic molecules such as threshold peaks, boomerang oscillations below the dissociative attachment threshold, or outer-well resonances.

  8. Vibrational excitation in molecule--surface collisions due to temporary negative molecular ion formation

    International Nuclear Information System (INIS)

    Gadzuk, J.W.

    1983-01-01

    Inelastic electron scattering from gaseous and physisorbed diatomic molecules results in greatly enhanced vibrational overtone excitation if the incident electron has the appropriate energy to form a shape-resonance-induced temporary negative molecular ion. It is proposed here that due to the image potential lowering of the electron affinity level of a diatomic molecule in interaction with a metal surface, somewhere outside the surface an incident molecule would find its affinity level degenerate with or lower than the substrate Fermi level at which point a substrate electron could hop onto the molecule, in analogy with gas phase harpooning processes. A negative molecular ion is thus formed which remains until the molecular ion reflects from the surface and the affinity level rises above the Fermi level, thus permitting reverse electron hopping back into the metal. The lifetime of the molecular ion can be controlled by varying both the kinetic energy of the incident molecule and also the substrate work function. In analogy with the electron scattering events, greatly enhanced vibrational excitation of overtones is expected in the molecules of the scattered beam. Induced fluorescence probing of the vibrational state distribution should then yield fundamental information pertaining to the dynamics of charge transfer reactions and nonadiabatic effects in molecule--surface interactions. A theory of this phenomenon is here presented together with the numerical consequences for a model system designed to simulate N 2 or NO scattering from standard surface science metal surfaces

  9. Red-light initiated atmospheric reactions of vibrationally excited molecules.

    Science.gov (United States)

    Vaida, V; Donaldson, D J

    2014-01-21

    We present a brief review of long wavelength, red-light initiated chemistry from excited vibrational levels of the ground electronic state of atmospheric trace species. When sunlight driven electronic state reactions are not effective, photochemical processes occurring by vibrational overtone excitation have been found to be important in reactions of oxidized atmospheric compounds (acids, alcohols and peroxides) prevalent in the Earth's atmosphere. This review focuses on the fundamental energetic, mechanistic and dynamical aspects of unimolecular reactions of vibrationally excited atmospheric species. We will discuss the relevance of these red light initiated reactions to address the discrepancies between atmospheric measurements and results of standard atmospheric models.

  10. Electron-molecule interactions and their applications

    CERN Document Server

    Christophorou, L G

    1984-01-01

    Electron-Molecule Interactions and Their Applications, Volume 2 provides a balanced and comprehensive account of electron-molecule interactions in dilute and dense gases and liquid media. This book consists of six chapters. Chapter 1 deals with electron transfer reactions, while Chapter 2 discusses electron-molecular positive-ion recombination. The electron motion in high-pressure gases and electron-molecule interactions from single- to multiple-collision conditions is deliberated in Chapter 3. In Chapter 4, knowledge on electron-molecule interactions in gases is linked to that on similar proc

  11. Coulomb excitation of highly charged projectile ions in relativistic collisions with diatomic molecules

    International Nuclear Information System (INIS)

    Artemyev, A. N.; McConnell, S. R.; Surzhykov, A.; Najjari, B.; Voitkiv, A. B.

    2011-01-01

    We investigate the Coulomb excitation of highly charged ions colliding with diatomic molecules. In this process, the coherent interaction between the projectile electron and two molecular centers may cause clear interference patterns in the (collision) energy dependencies of the total cross sections and alignment parameters. We discuss such a Young-type interference for the particular case of the K→L excitation of hydrogen- and helium-like projectile ions. Calculations, performed for the scattering of these ions on nitrogen molecules, indicate that the interference effects are extremely sensitive to the collisional geometry and are pronounced only if the molecular axis is aligned almost parallel to the incident beam trajectory.

  12. Effect resonance radiation transfer of excitation porous silicon to I sub 2 molecules sorbed in pores

    CERN Document Server

    Zakharchenko, K V; Kuznetsov, M B; Chistyakov, A A; Karavanskij, V A

    2001-01-01

    One studies the effect of resonance radiation-free transfer of electronic excitation between silicon nanocrystals and iodine molecules sorbed in pores. The experiment procedure includes laser-induced luminescence and laser desorption mass spectrometry. One analyzes photoluminescence spectra prior to and upon iodine sorption. Excitation of iodine through the mechanism of resonance transfer is determined to result in desorption of the iodine sorbed molecules with relatively high kinetic energies (3-1 eV). One evaluated the peculiar distance of resonance transfer the approximate value of which was equal to 2 nm

  13. Briefly on electronic excitation induced by radiation in a molecular target

    International Nuclear Information System (INIS)

    Bednar, J.

    1985-01-01

    Characteristic microscopic features of the absorption of photons and ionizing radiation by isolated molecules are called to mind of chemists and biologists. The elementary process of induction of electronic excitation localized on a single molecule has important bearing on collective excitation in condensed biological matter. (author)

  14. Electronic excitation and Auger spectroscopy of hexamethyldissilane

    International Nuclear Information System (INIS)

    Souza, G.G.B. de; Azevedo e Souza, A.C. de; Martins, R.J.; Lucas, C.A.

    1988-01-01

    In this work, it is presented an spectroscopic study of Si 2 (CH 3 ) 6 which presents interesting characteristics in the Si - Si bond. Electron energy loss technique was used in the energy range of 500 - 200 eV for the electron beam. Electronic excitation spectra were obtained for the energy loss range from 5 to 30 eV, and also Auger spectra. (A.C.A.S.) [pt

  15. An Exciting Aspect of Nanotechnology: Unimolecular Electronics

    Directory of Open Access Journals (Sweden)

    Metzger R. M.

    2013-08-01

    Full Text Available This is a brief update on our experimental work towards better one-molecule-thick monolayer rectifiers of electrical current, and on theoretical progress towards a one-molecule amplifier of electrical current. This program aims to provide electronic devices at the 2 to 3 nm level, as a dramatic advance towards practical integrated circuits of the future.

  16. Dissociative excitation and fragmentation of S8 by electron impact.

    Science.gov (United States)

    Brotton, S J; McConkey, J W

    2011-05-28

    The vacuum-ultraviolet emission spectrum from 136 nm to 168 nm following the dissociative excitation of a predominantly S(8) target by electron impact at 100 eV incident energy was measured. The relative cross sections for the dominant multiplets at 138.9, 142.9, 147.9, and 166.7 nm are presented. Excitation functions are shown for electron-impact energies from below threshold to 360 eV for the two most prominent emissions at 142.5 nm and 147.4 nm. Five thresholds are clearly apparent in both excitation functions. For the four highest energy channels, the energy separation between the adjacent thresholds is approximately constant and the cross sections reduce regularly as the threshold energies increase. We suggest possible fragmentation pathways of the dissociating S(8) molecule that reproduce the energies of our observed thresholds. © 2011 American Institute of Physics

  17. Electronic excitation of Na atom by electron impact

    International Nuclear Information System (INIS)

    Bielschowsky, C.E.; Souza, G.G.B. de; Lucas, C.A.; Nogueira, J.C.

    1988-01-01

    Electronic excitation of the 3s-3p transition in the Na atom was studied by intermediate energy electron impact spectroscopy. Differential Cross Sections (DCS) and Generalized Oscillator Strenghts (GOS) were determined experimentally for 1 KeV electrons. Theoretical results within the First Born Approximation as well as Glauber theory, were also performed. (A.C.A.S.) [pt

  18. Orientation-dependent imaging of electronically excited quantum dots

    Science.gov (United States)

    Nguyen, Duc; Goings, Joshua J.; Nguyen, Huy A.; Lyding, Joseph; Li, Xiaosong; Gruebele, Martin

    2018-02-01

    We previously demonstrated that we can image electronic excitations of quantum dots by single-molecule absorption scanning tunneling microscopy (SMA-STM). With this technique, a modulated laser beam periodically saturates an electronic transition of a single nanoparticle, and the resulting tunneling current modulation ΔI(x0, y0) maps out the SMA-STM image. In this paper, we first derive the basic theory to calculate ΔI(x0, y0) in the one-electron approximation. For near-resonant tunneling through an empty orbital "i" of the nanostructure, the SMA-STM signal is approximately proportional to the electron density |φi) (x0,y0)|imaged. We then show experimentally that we can nudge quantum dots on the surface and roll them, thus imaging excited state electronic structure of a single quantum dot at different orientations. We use density functional theory to model ODMs at various orientations, for qualitative comparison with the SMA-STM experiment. The model demonstrates that our experimentally observed signal monitors excited states, localized by defects near the surface of an individual quantum dot. The sub-nanometer super-resolution imaging technique demonstrated here could become useful for mapping out the three-dimensional structure of excited states localized by defects within nanomaterials.

  19. Molecule-by-Molecule Writing Using a Focused Electron Beam

    DEFF Research Database (Denmark)

    Van Dorp, Willem F.; Zhang, Xiaoyan; Feringa, Ben L.

    2012-01-01

    atoms also be written with an electron beam? We verify this with focused electron-beam-induced deposition (FEBID), a direct-write technique that has the current record for the smallest feature written by (electron) optical lithography. We show that the deposition of an organometallic precursor...... on graphene can be followed molecule-by-molecule with FEBID. The results show that mechanisms that are inherent to the process inhibit a further increase in control over the process. Hence, our results present the resolution limit of (electron) optical lithography techniques. The writing of isolated...

  20. Renormalization of Optical Excitations in Molecules near a Metal Surface

    DEFF Research Database (Denmark)

    García Lastra, Juan Maria; Thygesen, Kristian Sommer

    2011-01-01

    The lowest electronic excitations of benzene and a set of donor-acceptor molecular complexes are calculated for the gas phase and on the Al(111) surface using the many-body Bethe-Salpeter equation. The energy of the charge-transfer excitations obtained for the gas phase complexes are found...... consequence we find that close to the metal surface the optical gap of benzene can exceed its quasiparticle gap. A classical image charge model for the screened Coulomb interaction can account for all these effects which, on the other hand, are completely missed by standard time-dependent density functional...

  1. Stability of two-electron diatomic molecules

    International Nuclear Information System (INIS)

    Ferron, Alejandro; Serra, Pablo

    2007-01-01

    We present a detailed study of the ground state behaviour of two-electron diatomic molecules. The ground state stability diagram for diatomic molecules in the Born-Oppenheimer approximation is obtained and the behaviour of the ground state near the stability line is studied. Two different cases are analysed: the homonuclear two-centre two-electron molecule with the internuclear distance as a free parameter and the diatomic two-electron molecule (in this case, the internuclear distance is determined by equilibrium conditions). Analytical and numerical results for these systems are presented

  2. Electron spectroscopy of collisional excited atoms

    International Nuclear Information System (INIS)

    Straten, P. van der.

    1987-01-01

    In this thesis measurements are described in which coincidences are detected between scattered projectiles and emitted electrons. This yields information on two-electron excitation processes. In order to show what can be learnt from coincidence experiments a detailed theoretical analysis is given. The transition amplitudes, which contain all the information, are introduced (ch.2). In ch.3 the experimental set-up is shown. The results for the Li + -He system are shown in ch. 7 and are compared with predictions based on the Molecular-Orbitalmodel which however does not account for two-excitation mechanisms. With the transition amplitudes also the wave function of the excited atom has been completely determined. In ch.8 the shape of the electron cloud, induced by the collision, is derived from the amplitudes. The relation between the oscillatory motion of this cloud after the collision and the correlation between the two electrons of the excited atom is discussed. In ch. 6 it is shown that the broad structures in the non-coincident energy spectra of the Li + -He system are erroneously interpretated as a result of electron emission from the (Li-He) + -quasimolecule. A model is presented which explains, based on the results obtained from the coincidence measurements, these broad structures. In ch. 4 the Post-Collision Interaction process is treated. It is shown that for high-energy collisions, in contrast with general assumptions, PCI is important. In ch. 5 the importance of PCI-processes in photoionization of atoms, followed by Auger decay, are studied. From the formulas derived in ch. 4 simple analytical results are obtained. These are applied to recent experiments and good agreement is achieved. 140 refs.; 55 figs.; 9 tabs

  3. Electron impact excitation of potassium and sodium

    International Nuclear Information System (INIS)

    Phelps, J.O. III.

    1981-01-01

    Absolute electron-impact optical excitation functions of 24 transitions of the sharp, principal, diffuse and fundamental series of potassium have been measured in the impact energy range 0 to 400 eV. The determination of the target atom number density was made by measuring the transmissions of potassium resonance radiation from a fluorescence cell upon passage through the collision chamber. Direct excitation cross section of 14 states (5S, 6S, 7S, 8S, 4P, 5P, 6P, 7P, 3D, 5D, 6D, 5F, 6F, and 7F) have been determined from the measured optical excitation cross sections with the aid of radiative transition probabilities taken from the literature. These direct cross section results are compared with theoretical calculations based upon the Born approximation and the multi-state close-couplng approximation. Measurements were also made of the polarization of resolved components of the 4P-4S and 3D-4P doublets, and from these results the direct excitation functions of the separate orbital magnetic substates of the 3P state have been determined. This work has been extended to sodium, yielding measurements of optical excitation functions of 26 transitions of the sharp, principal, diffuse, fundamental, and nP-4S series in the energy range 0 to 150 eV. From these measurements, direct excitation functions of 14 states (4S, 5S, 6S, 7S, 3P, 4P, 5P, 6P, 3D, 4D, 5D, 6D, 6F, and 7F) have been determined. These are compared with theoretical results based on the Born approximation and the close-coupling method. Polarization measurements were made for several sharp, principal, and diffuse doublets, and this data is applied to determine the magnetic substate direct substate direct excitation functions for the 3P state

  4. The origin of small and large molecule behavior in the vibrational relaxation of highly excited molecules

    International Nuclear Information System (INIS)

    Gordon, R.J.

    1990-01-01

    An explanation is proposed for the qualitatively different types of behavior that have been reported for the vibrational relaxation of highly excited diatomic and polyatomic molecules. It is argued that all of the diatomic molecules that have been studied in bulk relax adiabatically at room temperature. In contrast, large polyatomic molecules have low frequency modes which act at ''doorway'' modes for the rest of the molecules, producing an impulsive relaxation mechanism. The theoretical work of Nesbitt and Hynes showed that impulsive collisions result in an exponential decay of the average vibrational energy of a Morse oscillator, whereas adiabatic collisions produce nonexponential power law behavior. We propose that this result explains a large body of data for the vibrational relaxation of small and large molecules

  5. selective excitation of vibrational modes of polyatomic molecule

    Indian Academy of Sciences (India)

    vnautiyal@himalaya.du.ac.in; sneh@del2.vsnl.net.in. MS received 3 September 2003; accepted 12 December 2003. Abstract. Mode-selective dynamics of triatomic molecule in the electronic ground state under continuous wave laser pulse is investigated for the discrete vibrational bound states. A non-perturbative approach ...

  6. Nature of electronic excitations in pentaerythritol tetranitrate crystals doped with 9,10-phenanthrenequinone

    Science.gov (United States)

    Garifzianova, Guzel; Tsyshevskiy, Roman; Zverev, Anton; Mitrofanov, Anatoly; Kuklja, Maija

    Electronic properties, optical absorption and chemical reactivity of organic ketones and quinone molecules have been widely studied because of their ability to abstract hydrogen atoms from other organic molecules once excited to the highly reactive 3(n, π*) state. Most of these studies were done for liquid solutions. In this joint theoretical and experimental study, we focused on excited states of pentaerythritol tetranitrate (PETN) crystals doped with 9,10-phenanthrenequinone (PQ) molecules. We explored electronic properties of the system and estimated energies of the electronic excitations. It was found that PQ molecule in its excited triplet state can catalyze unusual decomposition pathways of PETN, which are not attainable through the potential surface of the ground state. We discuss mechanisms of such autocatalytic reactions in PETN-PQ complexes. Research is supported by the US ONR (Grants N00014-16-1-2069 and N00014-16-1-2346) and NSF. We used NERSC, XSEDE and MARCC computational resources.

  7. Influence of capture to excited states of multiply charged ion beams colliding with small molecules

    International Nuclear Information System (INIS)

    Montenegro, P; Monti, J M; Fojón, O A; Hanssen, J; Rivarola, R D

    2015-01-01

    Electron capture by multiply charged ions impacting on small molecules is theoretically investigated. Particular attention is paid to the case of biological targets. The interest is focused on the importance of the transition to excited final states which can play a dominant role on the total capture cross sections. Projectiles at intermediate and high collision energies are considered. Comparison with existing experimental data is shown. (paper)

  8. Single Molecule Spectroscopy of Electron Transfer

    International Nuclear Information System (INIS)

    Holman, Michael; Zang, Ling; Liu, Ruchuan; Adams, David M.

    2009-01-01

    The objectives of this research are threefold: (1) to develop methods for the study electron transfer processes at the single molecule level, (2) to develop a series of modifiable and structurally well defined molecular and nanoparticle systems suitable for detailed single molecule/particle and bulk spectroscopic investigation, (3) to relate experiment to theory in order to elucidate the dependence of electron transfer processes on molecular and electronic structure, coupling and reorganization energies. We have begun the systematic development of single molecule spectroscopy (SMS) of electron transfer and summaries of recent studies are shown. There is a tremendous need for experiments designed to probe the discrete electronic and molecular dynamic fluctuations of single molecules near electrodes and at nanoparticle surfaces. Single molecule spectroscopy (SMS) has emerged as a powerful method to measure properties of individual molecules which would normally be obscured in ensemble-averaged measurement. Fluctuations in the fluorescence time trajectories contain detailed molecular level statistical and dynamical information of the system. The full distribution of a molecular property is revealed in the stochastic fluctuations, giving information about the range of possible behaviors that lead to the ensemble average. In the case of electron transfer, this level of understanding is particularly important to the field of molecular and nanoscale electronics: from a device-design standpoint, understanding and controlling this picture of the overall range of possible behaviors will likely prove to be as important as designing ia the ideal behavior of any given molecule.

  9. Double resonance spectroscopy of multiple-photon excited molecules

    Science.gov (United States)

    Steinfeld, J. I.; Melzer, J. E.

    1977-01-01

    Multiple infrared photon absorption is a quite general process which molecules can undergo when placed in a high flux of infrared energy, such as the focussed beam of a CO2 laser. In order to understand how this process works, one must be able to follow the evolution of the molecules through their internal states, populated by photon absorption. Double-resonance spectroscopy is the method of a choice for getting at this information. A system pumped by CO2 laser radiation can be examined with a tunable laser probe beam, such as that from a lead-salt diode laser. From such an experiment, one can directly observe Rabi modulation of the absorption lines, determine elementary state-to-state relaxation pathways, and locate higher excited vibrational states. Systems currently under investigation include SF6 and vinyl chloride. In suitable cases, the probe beam can be a tunable visible or UV source, such as a dye laser. Fluorescence spectroscopy can then be used to monitor the transient absorptions produced by multiple-photon excitation. Among the systems which can be examined are biacetyl and glyoxal.

  10. Solvent Effects on Electronic Excitations of an Organic Chromophore.

    Science.gov (United States)

    Zuehlsdorff, T J; Haynes, P D; Hanke, F; Payne, M C; Hine, N D M

    2016-04-12

    In this work we study the solvatochromic shift of a selected low-energy excited state of alizarin in water by using a linear-scaling implementation of large-scale time-dependent density functional theory (TDDFT). While alizarin, a small organic dye, is chosen as a simple example of solute-solvent interactions, the findings presented here have wider ramifications for the realistic modeling of dyes, paints, and pigment-protein complexes. We find that about 380 molecules of explicit water need to be considered in order to yield an accurate representation of the solute-solvent interaction and a reliable solvatochromic shift. By using a novel method of constraining the TDDFT excitation vector, we confirm that the origin of the slow convergence of the solvatochromic shift with system size is due to two different effects. The first factor is a strong redshift of the excitation due to an explicit delocalization of a small fraction of the electron and the hole from the alizarin onto the water, which is mainly confined to within a distance of 7 Å from the alizarin molecule. The second factor can be identified as long-range electrostatic influences of water molecules beyond the 7 Å region on the ground-state properties of alizarin. We also show that these electrostatic influences are not well reproduced by a QM/MM model, suggesting that full QM studies of relatively large systems may be necessary in order to obtain reliable results.

  11. Electron attachment to Van der Waals molecules

    International Nuclear Information System (INIS)

    Hatano, Y.

    1986-01-01

    A survey is given of recent experimental studies of low-energy electron attachment to O 2 , N 2 O and other molecules in dense gases and in sonic nozzle beams with emphasis on the important role of pre-existing van der Waals molecules in the attachment mechanism. The experimental results particularly for O 2 are compared with recent theories. A survey is also given briefly of recent studies on electron solvation and localization in the condensed phase from the viewpoint of the studies on electron interaction with van der Waals molecules. (Auth.)

  12. Electron-induced excitation of 93Mo

    Science.gov (United States)

    Chiara, C. J.; Carroll, J. J.; Marsh, J. C.; Matters, D. A.; Lane, G. J.; Hartley, D. J.; Polasik, M.; Rzadkiewicz, J.; Carpenter, M. P.; Greene, J. P.; Janssens, R. V. F.; Seweryniak, D.; Zhu, S.

    2016-09-01

    The inverse of the internal-conversion process, whereby a free electron is captured into an atomic orbital and subsequently excites the nucleus to a higher-lying state via a virtual energy exchange, was predicted to exist 40 years ago but has yet to be demonstrated experimentally. To search for this mode of nuclear excitation by electron capture, we performed an experiment at the ATLAS facility at Argonne National Laboratory. The t1/2 = 6.85-h, 21/2+ state of 93Mo was populated in the 7Li(90Zr, p 3 n) reaction. The excitation mechanism was predicted to induce depopulation of this isomer as the fast-moving 93mMo recoils slowed in the target material, emitting a characteristic sequence of γ rays in the process. Results of the search for these signature γ rays using Digital Gammasphere will be presented. This material is based upon work supported by the US DOE, Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User Facility.

  13. Many-body approach to electronic excitations concepts and applications

    CERN Document Server

    Bechstedt, Friedhelm

    2015-01-01

    The many-body-theoretical basis and applications of theoretical spectroscopy of condensed matter, e.g. crystals, nanosystems, and molecules are unified in one advanced text for readers from graduate students to active researchers in the field. The theory is developed from first principles including fully the electron-electron interaction and spin interactions. It is based on the many-body perturbation theory, a quantum-field-theoretical description, and Green's functions. The important expressions for ground states as well as electronic single-particle and pair excitations are explained. Based on single-particle and two-particle Green's functions, the Dyson and Bethe-Salpeter equations are derived. They are applied to calculate spectral and response functions. Important spectra are those which can be measured using photoemission/inverse photoemission, optical spectroscopy, and electron energy loss/inelastic X-ray spectroscopy. Important approximations are derived and discussed in the light of selected computa...

  14. Vibrationally coupled electron transport through single-molecule junctions

    Energy Technology Data Exchange (ETDEWEB)

    Haertle, Rainer

    2012-04-26

    vibrational effects have a profound influence on the transport characteristics of a single-molecule contact and play therefore a fundamental role in this transport problem. Our findings demonstrate that vibrationally coupled electron transport through a molecular junction involves two types of processes: (i) transport processes, where an electron tunnels through the molecular bridge from one lead to the other, and (ii) electron-hole pair creation processes, where an electron tunnels from one of the leads onto the molecular bridge and back to the same lead again. Transport processes directly contribute to the electrical current flowing through a molecular contact and involve both excitation and deexcitation processes of the vibrational modes of the junction. Electron-hole pair creation processes do not directly contribute to the electrical current and typically involve only deexcitation processes. Nevertheless, they constitute a cooling mechanism for the vibrational modes of a single-molecule junction that is as important as cooling by transport processes. As the level of vibrational excitation determines the efficiency of electron transport processes, they have an indirect influence on the electrical current flowing through the junction. As we show, however, this influence can be substantial, in particular, if the molecule is coupled asymmetrically to the leads. Accounting for all these processes and their complex interrelationship, we analyze a number of intriguing transport phenomena, including rectification, negative differential resistance, anomalous peak broadening, mode-selective vibrational excitation and vibrationally induced decoherence. Moreover, we show that higher levels of vibrational excitation are obtained for weaker electronic-vibrational coupling. Thus, based on physical grounds, we establish a relation between the weak electronic-vibrational coupling limit and the limit of large bias voltages, where the level of vibrational excitation in a molecular junction

  15. Excited States of the Diatomic Molecule CrHe

    Science.gov (United States)

    Pototschnig, Johann V.; Ratschek, Martin; Hauser, Andreas W.; Ernst, Wolfgang E.

    2013-06-01

    Chromium (Cr) atoms embedded in superfluid helium nanodroplets (He_N) have been investigated by laser induced fluorescence, beam depletion and resonant two-photon ionization spectroscopy in current experiments at our institute. Cr is found to reside inside the He_N in the a^7S ground state. Two electronically excited states, z^7P and y^7P, are involved in a photoinduced ejection process which allowed us to study Fano resonances in the photoionisation spectra The need for a better understanding of the experimental observations triggered a theoretical approach towards the computation of electronically excited states via high-level methods of computational chemistry. Two well-established, wave function-based methods, CASSCF and MRCI, are combined to calculate the potential energy curves for the three states involved. The character of the two excited states z^7P and y^7P turns out to be significantly different. Theory predicts the ejection of the Cr atom in the case of an y^7P excitation as was observed experimentally. The quasi-inert helium environment is expected to weaken spin selection rules, allowing a coupling between different spin states especially during the ejection process. We therefore extend our theoretical analysis to the lowest state in the triplet- and quintet- manifold. Most of these alternative states show very weak bonding of only a few wn. A. Kautsch, M. Hasewend, M. Koch and W. E. Ernst, Phys. Rev. A 86, 033428 (2012). A. Kautsch, M. Koch and W. E. Ernst, J. Phys. Chem. A, accepted, doi:10.1021/jp312336m}.

  16. Excitation of nitrogen molecules by the impact of 80-160 keV protons

    International Nuclear Information System (INIS)

    Itoh, Akio; Asari, Masatoshi; Fukuzawa, Fumio

    1977-01-01

    A new method of measuring the light intensity which is emitted following the impact of charged particles on gaseous molecules is presented in this paper. The principle of this method is based on the different spatial distributions of hydrogen atoms and secondary electrons. A cockcroft-Walton accelerator was used for the production of proton beam. The beam passed through a collision chamber which had two quartz windows. The pressure in the collision chamber was measured with either an ionization gauge or a Pirani gauge. The light intensity from the excited gas molecules was measured through the quartz windows with a movable optical system, and was spectrally analyzed with a monochromater. The light emission from nitrogen molecules excited by the impact of 80-160 KeV protons was studied over a wave length ranging from 3300 to 5400 x 10 -8 cm. In one of the measured spectra of photons, the vibrational bands of the N 2 + first negative system and of the second positive system were observed as prominent lines. These states seemed to be excited directly from the ground state of N2. By analyzing the light intensity, it can be said that the second positive state has singlet-triplet mixing and is excited mainly by secondary processes. (Kato, T.)

  17. Interactions of electrons with biologically important molecules

    International Nuclear Information System (INIS)

    Pisklova, K.; Papp, P.; Stano, M.

    2012-01-01

    For the study of interactions of low-energy electrons with the molecules in the gas phase, the authors used electron-molecule cross-beam apparatus. The experiment is carried out in high vacuum, where molecules of the tested compound are inducted through a capillary. For purposes of this experiment the sample was electrically heated to 180 Deg C., giving a bundle of GlyGly molecules into the gas phase. The resulting signals can be evaluated in two different modes: mass spectrum - at continuous electron energy (e.g. 100 eV) they obtained the signal of intensity of the ions according to their mass to charge ratio; ionization and resonance spectra - for selected ion mass when the authors received the signal of intensity of the ions, depending on the energy of interacting electron.

  18. Excited state electron affinity calculations for aluminum

    Science.gov (United States)

    Hussein, Adnan Yousif

    2017-08-01

    Excited states of negative aluminum ion are reviewed, and calculations of electron affinities of the states (3s^23p^2)^1D and (3s3p^3){^5}{S}° relative to the (3s^23p)^2P° and (3s3p^2)^4P respectively of the neutral aluminum atom are reported in the framework of nonrelativistic configuration interaction (CI) method. A priori selected CI (SCI) with truncation energy error (Bunge in J Chem Phys 125:014107, 2006) and CI by parts (Bunge and Carbó-Dorca in J Chem Phys 125:014108, 2006) are used to approximate the valence nonrelativistic energy. Systematic studies of convergence of electron affinity with respect to the CI excitation level are reported. The calculated value of the electron affinity for ^1D state is 78.675(3) meV. Detailed Calculations on the ^5S°c state reveals that is 1216.8166(3) meV below the ^4P state.

  19. Advanced cold molecule electron EDM

    Directory of Open Access Journals (Sweden)

    Campbell Wesley C.

    2013-08-01

    Full Text Available Measurement of a non-zero electric dipole moment (EDM of the electron within a few orders of magnitude of the current best limit of |de| < 1.05 × 10−27 e⋅cm [1] would be an indication of physics beyond the Standard Model. The ACME Collaboration is searching for an electron EDM by performing a precision measurement of electron spin precession in the metastable H3Δ1 state of thorium monoxide (ThO using a slow, cryogenic beam. We discuss the current status of the experiment. Based on a data set acquired from 14 hours of running time over a period of 2 days, we have achieved a 1-sigma statistical uncertainty of δde = 1 × 10−28 e⋅cm/√T, where T is the running time in days.

  20. Process and system for isotope separation using the selective vibrational excitation of molecules

    International Nuclear Information System (INIS)

    Woodroffe, J.A.; Keck, J.C.

    1976-01-01

    This invention concerns the separation of isotopes by using the isotopically selective vibrational excitation and the vibration-translation reactions of the excited particles. UF 6 molecular mixed with a carrier gas, such as argon, are directed through a refrigerated chamber lighted by a laser radiation tuned to excite vibrationally the uranium hexafluoride molecules of a particular uranium isotope. The density of the carrier gas is preferably maintained above the density of the uranium hexafluoride to allow a greater collision probability of the vibrationally excited molecules with a carried molecule. In such a case, the vibrationally excited uranium hexafluoride will collide with a carrier gas molecule provoking the conversion of the excitation energy into a translation of the excited molecule, resulting in thermal energy or greater diffusibility than that of the other uranium hexafluoride molecules [fr

  1. Application of scattering quantum theory for simple chemical reaction calculations. Electron scattering by biatomic molecules

    International Nuclear Information System (INIS)

    Pozdneev, S.A.; Shcheglov, V.A.

    1987-01-01

    Theory of multiple scattering in the three-body system, which mathematical base is L.D. Fadeev's equations, is applied for calculating the simplest chemical reactions proceeding in electron collision with two-atom molecules. Calculations of cross sections of elastic scattering, excitation, dissociation and dissociative electron attachment to two-atom molecules being in different excited rotational-vibrational states have been performed on the basis of the developed theory

  2. Search for Excited Electrons with ATLAS at LHC

    CERN Document Server

    Cakir, O; Mehdiyev, R

    2001-01-01

    We study the single production of excited electrons at teh CERN LHC through contact interactions of fermions. Subsequent decays of excited leptons to ordinary leptons and electrowek gauge bosons via gauge interactions are examined, Excited single electrons could be accessible up to a mass range of 1.0-4.0 TeV at LHC.

  3. Gaseous Electronics Tables, Atoms, and Molecules

    CERN Document Server

    Raju, Gorur Govinda

    2011-01-01

    With the constant emergence of new research and application possibilities, gaseous electronics is more important than ever in disciplines including engineering (electrical, power, mechanical, electronics, and environmental), physics, and electronics. The first resource of its kind, Gaseous Electronics: Tables, Atoms, and Molecules fulfills the author's vision of a stand-alone reference to condense 100 years of research on electron-neutral collision data into one easily searchable volume. It presents most--if not all--of the properly classified experimental results that scientists, researchers,

  4. Electron impact ionization-excitation of Helium

    Science.gov (United States)

    Ancarani, Lorenzo Ugo; Gomez, A. I.; Gasaneo, G.; Mitnik, D. M.; Ambrosio, M. J.

    2016-09-01

    We calculate triple differential cross sections (TDCS) for the process of ionization-excitation of Helium by fast electron impact in which the residual ion is left in the n =2 excited state. We chose the strongly asymmetric kinematics used in the experiment performed by Dupré et al.. In a perturbative scheme, for high projectile energies the four-body problem reduces to a three-body one and, within that framework, we solve the time- independent Schrödinger equation with a Sturmian approach. The method, based on Generalized Sturmian Functions (GSF), is employed to obtain the initial ground state of Helium, the single-continuum state and the scattering wave function; for each of them, the GSF basis is constructed with the corresponding adequate asymptotic conditions. Besides, the method presents the following advantage: the scattering amplitudes can be extracted directly in the asymptotic region of the scattering solution, and thus the TDCS can be obtained without requiring a matrix element evaluation.

  5. Collective electronic excitations in C60 crystals

    International Nuclear Information System (INIS)

    Wu, X.; Ulloa, S.E.

    1994-01-01

    We present a theoretical study of the electronic excitations in fullerene crystals by calculating the density-density correlation function in a fully nonlocal linear response theory. Our results indicate that the collective features associates with the π→π * transitions show strong anisotropic properties, with peaks changing by as much as 0.7 eV in different directions. Meanwhile, the calculated mode dispersion exhibits rather weak wave-number dependence along a given direction, in general agreement with experimental results. The oscillator strength also shows anisotropic behavior, with significant weight redistribution for different directions. We also analyze this system in terms of a classical point-dipole array model, and show that this simple model approximates well the quantum results

  6. Multiphoton excitations in vibrational rotational states of diatomic molecules in intense electromagnetic field

    Science.gov (United States)

    Faisal, F. H. M.; Rahman, N. K.

    1972-01-01

    A theory is presented and a calculational procedure is outlined for evaluating transition amplitudes of multiphoton excitations of vibrational-rotational levels in diatomic molecules. This theory can be utilized in studying behavior of molecules in intense electromagnetic fields.

  7. Multiple-photon excitation and dissociation of polyatomic molecules

    International Nuclear Information System (INIS)

    Cantrell, C.D.

    1986-01-01

    This book is Volume 35 in Springer's Topics in Current Physics series designed to provide the interested reader perspective on a rapidly developing research field by gathering together review articles by major players. The editor has accurately highlighted the major results of the multiple-photon excitation (MPE) shock wave of research activity that propagated through the gas-phase chemical physics community during the 1970's. Throughout this period three questions intrigued the photochemists: (1) how is it possible that virtually any polyatomic molecule can efficiently absorb scores of infrared photons from a pulsed CO 2 TEA laser to achieve bond fission? (2) can insight into the dissociation dynamic be gained from this process, and in particular can bonds be made to break selectively? (3) could MPE be used to separate heavy isotopes? The answers to the first two questions are thoroughly examined and answered in the excellent review by Y.T. Lee et al., which itself is worth the price of the book. The question of isotope separation is discussed in two articles, one by Ambartzumian and the other by Cantrell. However, the recent glut of cheap uranium on world energy markets and the decision of DOE to develop atomic multiphoton ionization as the process of choice have resulted in a rapid deflation of interest in MPE separation schemes

  8. Nuclear dynamics in resonant electron collisions with small polyatomic molecules

    International Nuclear Information System (INIS)

    Rescigno, T N; McCurdy, C W; Haxton, D J; Trevisan, C S; Orel, A E

    2007-01-01

    The excitation and dissociation of polyatomic molecules by low-energy electron impact can be dominated by resonant collision processes. The formal resonance theory that has formed the basis for much of our understanding of these processes has, for the most part, treated the nuclear dynamics in one dimension. This talk will focus on dramatic effects in low energy electron scattering by small molecules that are purely polyatomic in origin and that can only be studied with a multi-dimensional treatment of the dissociation dynamics. Resonant vibrational excitation of CO 2 and dissociative electron attachment to formic acid are briefly described to illustrate the discussion. The talk will then concentrate on the recent progress that has been made in studying dissociative electron attachment to water, including a completely ab initio evaluation of the three complex-valued resonance potential surfaces involved as well as the dynamical studies, carried out in full dimensionality, that give the state-specific cross sections and branching ratios into various two- and three-body channels

  9. Electronic structure of molecules using relativistic effective core potentials

    International Nuclear Information System (INIS)

    Hay, P.J.

    1981-01-01

    Starting with one-component Cowan-Griffin relativistic Hartree-Fock orbitals, which successfully incorporate the mass-velocity and Darwin terms present in more complicated wavefunctions such as Dirac-Hartree-Fock, one can derive relativistic effective core potentials (RECP's) to carry out molecular calculations. These potentials implicitly include the dominant relativistic terms for molecules while allowing one to use the traditional quantum chemical techniques for studying the electronic structure of molecules. The effects of spin-orbit coupling can then be included using orbitals from such calculations using an effective 1-electron, 1-center spin-orbit operator. Applications to molecular systems involving heavy atoms, show good agreement with available spectroscopic data on molecular geometries and excitation energies

  10. Non-adiabatic Excited State Molecule Dynamics Modeling of Photochemistry and Photophysics of Materials

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, Tammie Renee [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tretiak, Sergei [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-01-06

    Understanding and controlling excited state dynamics lies at the heart of all our efforts to design photoactive materials with desired functionality. This tailor-design approach has become the standard for many technological applications (e.g., solar energy harvesting) including the design of organic conjugated electronic materials with applications in photovoltaic and light-emitting devices. Over the years, our team has developed efficient LANL-based codes to model the relevant photophysical processes following photoexcitation (spatial energy transfer, excitation localization/delocalization, and/or charge separation). The developed approach allows the non-radiative relaxation to be followed on up to ~10 ps timescales for large realistic molecules (hundreds of atoms in size) in the realistic solvent dielectric environment. The Collective Electronic Oscillator (CEO) code is used to compute electronic excited states, and the Non-adiabatic Excited State Molecular Dynamics (NA-ESMD) code is used to follow the non-adiabatic dynamics on multiple coupled Born-Oppenheimer potential energy surfaces. Our preliminary NA-ESMD simulations have revealed key photoinduced mechanisms controlling competing interactions and relaxation pathways in complex materials, including organic conjugated polymer materials, and have provided a detailed understanding of photochemical products and intermediates and the internal conversion process during the initiation of energetic materials. This project will be using LANL-based CEO and NA-ESMD codes to model nonradiative relaxation in organic and energetic materials. The NA-ESMD and CEO codes belong to a class of electronic structure/quantum chemistry codes that require large memory, “long-queue-few-core” distribution of resources in order to make useful progress. The NA-ESMD simulations are trivially parallelizable requiring ~300 processors for up to one week runtime to reach a meaningful restart point.

  11. Electron delocalization and aromaticity in low-lying excited states of archetypal organic compounds.

    Science.gov (United States)

    Feixas, Ferran; Vandenbussche, Jelle; Bultinck, Patrick; Matito, Eduard; Solà, Miquel

    2011-12-14

    Aromaticity is a property usually linked to the ground state of stable molecules. Although it is well-known that certain excited states are unquestionably aromatic, the aromaticity of excited states remains rather unexplored. To move one step forward in the comprehension of aromaticity in excited states, in this work we analyze the electron delocalization and aromaticity of a series of low-lying excited states of cyclobutadiene, benzene, and cyclooctatetraene with different multiplicities at the CASSCF level by means of electron delocalization measures. While our results are in agreement with Baird's rule for the aromaticity of the lowest-lying triplet excited state in annulenes having 4nπ-electrons, they do not support Soncini and Fowler's generalization of Baird's rule pointing out that the lowest-lying quintet state of benzene and septet state of cyclooctatetraene are not aromatic.

  12. Electron impact excitation of helium atom

    Science.gov (United States)

    Han, Xiao-Ying; Zeng, De-Ling; Gao, Xiang; Li, Jia-Ming

    2015-08-01

    A method to deal with the electron impact excitation cross sections of an atom from low to high incident energies are presented. This method combines the partial wave method and the first Born approximation (FBA), i.e., replacing the several lowest partial wave cross sections of the total cross sections within FBA by the corresponding exact partial wave cross sections. A new set of codes are developed to calculate the FBA partial wave cross sections. Using this method, the convergent e-He collision cross sections of optical-forbidden and optical-allowed transitions at low to high incident energies are obtained. The calculation results demonstrate the validity and efficiency of the method. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921501 and 2013CB922200), the National Natural Science Foundation of China (Grant Nos. 11274035, 11275029, 11328401, 11371218, 11474031, 11474032, and 11474034), and the Foundation of Development of Science and Technology of Chinese Academy of Engineering Physics (Grant Nos. 2013A0102005 and 2014A0102005).

  13. Resonant R-matrix theory of inelastic processes in collisions of electrons with HF molecules

    International Nuclear Information System (INIS)

    Fabrikant, I.I.; Kalin, S.A.; Kazansky, A.K.

    1992-01-01

    The resonant R-matrix theory is applied to the calculation of vibrational excitation and dissociative attachment cross sections in collisions of electrons with HF molecules. The parameters of our model were chosen by fitting our eigenphase sums for e-HF scattering to the results of ab initio R-matrix calculations by previous authors. Another set of parameters was chosen to get a better agreement with experimental results on vibrational excitation. Dissociative attachment cross sections calculated with these parameters are in good agreement with experimental results. We also calculated cross sections for vibrational excitation from excited states and angular distribution of the scattered electrons. (author)

  14. Time Resolved Energy Transfer and Photodissociation of Vibrationally Excited Molecules

    National Research Council Canada - National Science Library

    Crim, F. F

    2007-01-01

    ...) in solution and in the gas phase. This second experiment is one of the few direct comparisons of intramolecular vibrational energy flow in a solvated molecule with that in the same molecule isolated in a gas...

  15. Search for Excited Electrons in ep Collisions at HERA

    CERN Document Server

    Aaron, F.D.; Andreev, V.; Antunovic, B.; Aplin, S.; Asmone, A.; Astvatsatourov, A.; Bacchetta, A.; Backovic, S.; Baghdasaryan, A.; Baranov, P.; Barrelet, E.; Bartel, W.; Beckingham, M.; Begzsuren, K.; Behnke, O.; Belousov, A.; Berger, N.; Bizot, J.C.; Boenig, M.-O.; Boudry, V.; Bozovic-Jelisavcic, I.; Bracinik, J.; Brandt, G.; Brinkmann, M.; Brisson, V.; Bruncko, D.; Bunyatyan, A.; Buschhorn, G.; Bystritskaya, L.; Campbell, A.J.; Cantun Avila, K.B.; Cassol-Brunner, F.; Cerny, K.; Cerny, V.; Chekelian, V.; Cholewa, A.; Contreras, J.G.; Coughlan, J.A.; Cozzika, G.; Cvach, J.; Dainton, J.B.; Daum, K.; Deak, M.; de Boer, Y.; Delcourt, B.; Del Degan, M.; Delvax, J.; De Roeck, A.; De Wolf, E.A.; Diaconu, C.; Dodonov, V.; Dossanov, A.; Dubak, A.; Eckerlin, G.; Efremenko, V.; Egli, S.; Eliseev, A.; Elsen, E.; Essenov, S.; Falkiewicz, A.; Faulkner, P.J.W.; Favart, L.; Fedotov, A.; Felst, R.; Feltesse, J.; Ferencei, J.; Finke, L.; Fleischer, M.; Fomenko, A.; Gabathuler, E.; Gayler, J.; Ghazaryan, Samvel; Glazov, A.; Glushkov, I.; Goerlich, L.; Goettlich, M.; Gogitidze, N.; Gouzevitch, M.; Grab, C.; Greenshaw, T.; Grell, B.R.; Grindhammer, G.; Habib, S.; Haidt, D.; Hansson, M.; Helebrant, C.; Henderson, R.C.W.; Henschel, H.; Herrera, G.; Hildebrandt, M.; Hiller, K.H.; Hoffmann, D.; Horisberger, R.; Hovhannisyan, A.; Hreus, T.; Jacquet, M.; Janssen, M.E.; Janssen, X.; Jemanov, V.; Jonsson, L.; Johnson, D.P.; Jung, Andreas Werner; Jung, H.; Kapichine, M.; Katzy, J.; Kenyon, I.R.; Kiesling, C.; Klein, M.; Kleinwort, C.; Klimkovich, T.; Kluge, T.; Knutsson, A.; Kogler, R.; Korbel, V.; Kostka, P.; Kraemer, M.; Krastev, K.; Kretzschmar, J.; Kropivnitskaya, A.; Kruger, K.; Kutak, K.; Landon, M.P.J.; Lange, W.; Lastovicka-Medin, G.; Laycock, P.; Lebedev, A.; Leibenguth, G.; Lendermann, V.; Levonian, S.; Li, G.; Lipka, K.; Liptaj, A.; List, B.; List, J.; Loktionova, N.; Lopez-Fernandez, R.; Lubimov, V.; Lucaci-Timoce, A.-I.; Lytkin, L.; Makankine, A.; Malinovski, E.; Marage, P.; Marti, Ll.; Martyn, H.-U.; Maxfield, S.J.; Mehta, A.; Meier, K.; Meyer, A.B.; Meyer, H.; Meyer, H.; Meyer, J.; Michels, V.; Mikocki, S.; Milcewicz-Mika, I.; Moreau, F.; Morozov, A.; Morris, J.V.; Mozer, Matthias Ulrich; Mudrinic, M.; Muller, K.; Murin, P.; Nankov, K.; Naroska, B.; Naumann, Th.; Newman, Paul R.; Niebuhr, C.; Nikiforov, A.; Nowak, G.; Nowak, K.; Nozicka, M.; Olivier, B.; Olsson, J.E.; Osman, S.; Ozerov, D.; Palichik, V.; Panagoulias, I.; Pandurovic, M.; Papadopoulou, Th.; Pascaud, C.; Patel, G.D.; Pejchal, O.; Peng, H.; Perez, E.; Petrukhin, A.; Picuric, I.; Piec, S.; Pitzl, D.; Placakyte, R.; Polifka, R.; Povh, B.; Preda, T.; Radescu, V.; Rahmat, A.J.; Raicevic, N.; Raspiareza, A.; Ravdandorj, T.; Reimer, P.; Rizvi, E.; Robmann, P.; Roland, B.; Roosen, R.; Rostovtsev, A.; Rotaru, M.; Ruiz Tabasco, J.E.; Rurikova, Z.; Rusakov, S.; Salek, D.; Salvaire, F.; Sankey, D.P.C.; Sauter, M.; Sauvan, E.; Schmidt, S.; Schmitt, S.; Schmitz, C.; Schoeffel, L.; Schoning, A.; Schultz-Coulon, H.-C.; Sefkow, F.; Shaw-West, R.N.; Sheviakov, I.; Shtarkov, L.N.; Shushkevich, S.; Sloan, T.; Smiljanic, Ivan; Smirnov, P.; Soloviev, Y.; Sopicki, P.; South, D.; Spaskov, V.; Specka, Arnd E.; Staykova, Z.; Steder, M.; Stella, B.; Straumann, U.; Sunar, D.; Sykora, T.; Tchoulakov, V.; Thompson, G.; Thompson, P.D.; Toll, T.; Tomasz, F.; Tran, T.H.; Traynor, D.; Trinh, T.N.; Truol, P.; Tsakov, I.; Tseepeldorj, B.; Tsurin, I.; Turnau, J.; Tzamariudaki, E.; Urban, K.; Valkarova, A.; Vallee, C.; Van Mechelen, P.; Vargas Trevino, A.; Vazdik, Y.; Vinokurova, S.; Volchinski, V.; Wegener, D.; Wessels, M.; Wissing, Ch.; Wunsch, E.; Yeganov, V.; Zacek, J.; Zalesak, J.; Zhang, Z.; Zhelezov, A.; Zhokin, A.; Zhu, Y.C.; Zimmermann, T.; Zohrabyan, H.; Zomer, F.

    2008-01-01

    A search for excited electrons is performed using the full $e^{\\pm}p$ data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb$^{-1}$. The electroweak decays of excited electrons ${e}^{*}\\to{e}{\\gamma}$, ${e}^{*}\\to{e}Z$ and ${e}^{*}{\\to}\

  16. Electron correlation in molecules and condensed phases

    CERN Document Server

    March, N H

    1996-01-01

    This reference describes the latest research on correlation effects in the multicenter problems of atoms, molecules, and solids The author utilizes first- and second-order matrices, including the important observable electron density rho(r), and the Green function for discussing quantum computer simulations With its focus on concepts and theories, this volume will benefit experimental physicists, materials scientists, and physical and inorganic chemists as well as graduate students

  17. All Electron ab initio Investigations of the Electronic States of the MoN Molecule

    DEFF Research Database (Denmark)

    Shim, Irene; Gingerich, Karl A.

    1999-01-01

    The low lying electronic states of the molecule MoN have been investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) calculations. The relativistic corrections for the one electron Darwin contact term and the relativistic mass-velocity correction have...... been determined in perturbation calculations. The electronic ground state is confirmed as being 4 . The chemical bond of MoN has triple bond character due to the approximately fully occupied delocalized bonding and orbitals. The spectroscopic constants for the ground state and ten excited states have....... The spectroscopic constants for the 4 ground state have been determined as re = 1.636 Å and e = 1109 cm-1, and for the 4 state as re = 1.662 Å and e = 941 cm-1. The values for the ground state are in excellent agreement with available experimental data. The MoN molecule is polar with charge transfer from Mo to N...

  18. High Resolution Studies of Electron Attachment to Molecules

    International Nuclear Information System (INIS)

    Braun, M.; Ruf, M.-W.; Hotop, H.; Fabrikant, I. I.

    2009-01-01

    In this paper, we survey recent progress in studies of anion formation via (dissociative) electron attachment (DEA) to simple molecules, as measured with the laser photoelectron attachment (LPA) method at high resolution. The limiting (E→0) threshold behavior of the cross sections is elucidated for s-wave and p-wave attachment. Cusps at onsets for vibrational excitation (VE), due to interaction of the DEA channnel with the VE channel, are clearly detected, and vibrational Feshbach resonances just below vibrational onsets are observed for molecules with sufficiently strong long-range attraction between the electron and the molecule. From the LPA anion yields, absolute DEA cross sections (energy range typically E = 0.001-2 eV) are determined with reference to rate coefficients for thermal electron attachment at the appropriate gas temperature (normally T G = 300 K). The experimental data are compared with theoretical cross sections, calculated within the framework of an R-matrix or an Effective Range theory approach.

  19. Single-Molecule Interfacial Electron Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Wilson [Univ. of California, Irvine, CA (United States)

    2018-02-03

    Interfacial electron transfer (ET) plays an important role in many chemical and biological processes. Specifically, interfacial ET in TiO2-based systems is important to solar energy technology, catalysis, and environmental remediation technology. However, the microscopic mechanism of interfacial ET is not well understood with regard to atomic surface structure, molecular structure, bonding, orientation, and motion. In this project, we used two complementary methodologies; single-molecule fluorescence spectroscopy, and scanning-tunneling microscopy and spectroscopy (STM and STS) to address this scientific need. The goal of this project was to integrate these techniques and measure the molecular dependence of ET between adsorbed molecules and TiO2 semiconductor surfaces and the ET induced reactions such as the splitting of water. The scanning probe techniques, STM and STS, are capable of providing the highest spatial resolution but not easily time-resolved data. Single-molecule fluorescence spectroscopy is capable of good time resolution but requires further development to match the spatial resolution of the STM. The integrated approach involving Peter Lu at Bowling Green State University (BGSU) and Wilson Ho at the University of California, Irvine (UC Irvine) produced methods for time and spatially resolved chemical imaging of interfacial electron transfer dynamics and photocatalytic reactions. An integral aspect of the joint research was a significant exchange of graduate students to work at the two institutions. This project bridged complementary approaches to investigate a set of common problems by working with the same molecules on a variety of solid surfaces, but using appropriate techniques to probe under ambient (BGSU) and ultrahigh vacuum (UCI) conditions. The molecular level understanding of the fundamental interfacial electron transfer processes obtained in this joint project will be important for developing efficient light harvesting

  20. Fragmentation of excited molecules and ions in the radiolysis of hydrocarbons

    International Nuclear Information System (INIS)

    Shida, S.; Hatano, Y.

    1976-01-01

    A survey is given of recent studies of the primary C-H and C-C bond dissociations of excited molecules and ions in the gas-and liquid-phase radiolysis of hydrocarbons, which have been mainly carried out by the product analysis method. In the C-C bond dissociations evidence has been presented for the fragmentation of the excited parent ion, while in the C-H bond dissociations attention has been focused upon an important role of hot hydrogen atoms in the hydrogen formation. A theoretical treatment of highly excited hydrocarbon molecules involving super-excited states in also described. (author)

  1. Implications of electron attachment to highly-excited states in pulsed-power discharges

    International Nuclear Information System (INIS)

    Pinnaduwage, L.A.; Univ. of Tennessee, Knoxville, TN

    1997-01-01

    The author points out the possible implications of electron attachment to highly-excited states of molecules in two pulsed power technologies. One involves the pulsed H 2 discharges used for the generation of H ion beams for magnetic fusion energy and particle accelerators. The other is the power modulated plasma discharges used for material processing

  2. Search for excited charged leptons in electron positron collisions

    CERN Document Server

    Vachon, Brigitte Marie Christine; Sobie, Randall

    2002-01-01

    A search for evidence that fundamental particles are made of smaller subconstituents is performed. The existence of excited states of fundamental particles would be an unambiguous indication of their composite nature. Experimental signatures compatible with the production of excited states of charged leptons in electron-positron collisions are studied. The data analysed were collected by the OPAL detector at the LEP collider. No evidence for the existence of excited states of charged leptons was found. Upper limits on the product of the cross-section and the electromagnetic branching fraction are inferred. Using results from the search for singly produced excited leptons, upper limits on the ratio of the excited lepton coupling constant to the compositeness scale are calculated. From pair production searches, 95% confidence level lower limits on the masses of excited electrons, muons and taus are determined to be 103.2 GeV.

  3. All Electron ab initio Investigations of the Electronic States of the MoN Molecule

    DEFF Research Database (Denmark)

    Shim, Irene; Gingerich, Karl A.

    1999-01-01

    The low lying electronic states of the molecule MoN have been investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) calculations. The relativistic corrections for the one electron Darwin contact term and the relativistic mass-velocity correction have...... been derived. The excited doublet states, 2 , 2 , 2 , and 2 + are found to be lower lying than the 4 state that has been investigated experimentally. Elaborate multi configuration configuration interaction (MRCI) calculations have been carried out for the states 4 and 4 using various basis sets....... The spectroscopic constants for the 4 ground state have been determined as re = 1.636 Å and e = 1109 cm-1, and for the 4 state as re = 1.662 Å and e = 941 cm-1. The values for the ground state are in excellent agreement with available experimental data. The MoN molecule is polar with charge transfer from Mo to N...

  4. Electron attachment to indole and related molecules

    Science.gov (United States)

    Modelli, Alberto; Jones, Derek; Pshenichnyuk, Stanislav A.

    2013-11-01

    Gas-phase formation of temporary negative ion states via resonance attachment of low-energy (0-6 eV) electrons into vacant molecular orbitals of indoline (I), indene (II), indole (III), 2-methylen-1,3,3-trimethylindoline (IV), and 2,3,3-trimethyl-indolenine (V) was investigated for the first time by electron transmission spectroscopy (ETS). The description of their empty-level structures was supported by density functional theory and Hartree-Fock calculations, using empirically calibrated linear equations to scale the calculated virtual orbital energies. Dissociative electron attachment spectroscopy (DEAS) was used to measure the fragment anion yields generated through dissociative decay channels of the parent molecular anions of compounds I-V, detected with a mass filter as a function of the incident electron energy in the 0-14 eV energy range. The vertical and adiabatic electron affinities were evaluated at the B3LYP/6-31+G(d) level as the anion/neutral total energy difference. The same theoretical method is also used for evaluation of the thermodynamic energy thresholds for production of the negative fragments observed in the DEA spectra. The loss of a hydrogen atom from the parent molecular anion ([M-H]-) provides the most intense signal in compounds I-IV. The gas-phase DEAS data can provide support for biochemical reaction mechanisms in vivo involving initial hydrogen abstraction from the nitrogen atom of the indole moiety, present in a variety of biologically important molecules.

  5. Electronic excitation in ion-atom collisions

    International Nuclear Information System (INIS)

    Rodriguez, V.D.; Miraglia, J.E.

    1988-01-01

    Theoretical calculations for excitation of hydrogen-like atoms by ion impact at high and intermediate energies, are presented. Impulsive and eikonal wave functions are employed, both normalized. It is studied the dependence on energy and projectil charge (saturation) of cross sections, compared to experimental results. (A.C.A.S.) [pt

  6. Search for excited electrons in ep collisions at HERA

    Energy Technology Data Exchange (ETDEWEB)

    Aaron, F.D. [National Inst. for Physics and Nuclear Engineering (NIPNE), Bucharest (Romania)]|[Bucharest Univ. (Romania). Faculty of Physics; Alexa, C. [National Inst. for Physics and Nuclear Engineering (NIPNE), Bucharest (Romania); Andreev, V. [Lebedev Physical Inst., Moscow (RU)] (and others)

    2008-05-15

    A search for excited electrons is performed using the full e{sup {+-}}p data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb{sup -1}. The electroweak decays of excited electrons e{sup *} {yields}e{gamma}, e{sup *} {yields}eZ and e{sup *} {yields}{nu}W with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e{sup *} production cross sections and on the ratio f/{lambda} of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e{sup *} production via contact interactions is also addressed for the first time in ep collisions. (orig.)

  7. Predissociation and Quenching Dynamics of Electronically Excited Hydroxyl Radicals

    National Research Council Canada - National Science Library

    Lester, Marsha

    2004-01-01

    .... Significant progress has been made on three different fronts: (1) simulation of ultraviolet emission data from the Space Shuttle's thruster plume as originating from solar-induced and collision-induced electronic excitation of hydroxyl radicals; (2...

  8. Current status of free radicals and electronically excited metastable species as high energy propellants

    Science.gov (United States)

    Rosen, G.

    1973-01-01

    A survey is presented of free radicals and electronically excited metastable species as high energy propellants for rocket engines. Nascent or atomic forms of diatomic gases are considered free radicals as well as the highly reactive diatomic triatomic molecules that posess unpaired electrons. Manufacturing and storage problems are described, and a review of current experimental work related to the manufacture of atomic hydrogen propellants is presented.

  9. A ballistic transport model for electronic excitation following particle impact

    Science.gov (United States)

    Hanke, S.; Heuser, C.; Weidtmann, B.; Wucher, A.

    2018-01-01

    We present a ballistic model for the transport of electronic excitation energy induced by keV particle bombardment onto a solid surface. Starting from a free electron gas model, the Boltzmann transport equation (BTE) is employed to follow the evolution of the temporal and spatial distribution function f (r → , k → , t) describing the occupation probability of an electronic state k → at position r → and time t. Three different initializations of the distribution function are considered: i) a thermal distribution function with a locally and temporally elevated electron temperature, ii) a peak excitation at a specific energy above the Fermi level with a quasi-isotropic distribution in k-space and iii) an anisotropic peak excitation with k-vectors oriented in a specific transport direction. While the first initialization resembles a distribution function which may, for instance, result from electronic friction of moving atoms within an ion induced collision cascade, the peak excitation can in principle result from an autoionization process after excitation in close binary collisions. By numerically solving the BTE, we study the electronic energy exchange along a one dimensional transport direction to obtain a time and space resolved excitation energy distribution function, which is then analyzed in view of general transport characteristics of the chosen model system.

  10. Electron-vibron coupling effects on electron transport via a single-molecule magnet

    Science.gov (United States)

    McCaskey, Alexander; Yamamoto, Yoh; Warnock, Michael; Burzurí, Enrique; van der Zant, Herre S. J.; Park, Kyungwha

    2015-03-01

    We investigate how the electron-vibron coupling influences electron transport via an anisotropic magnetic molecule, such as a single-molecule magnet (SMM) Fe4, by using a model Hamiltonian with parameter values obtained from density-functional theory (DFT). The magnetic anisotropy parameters, vibrational energies, and electron-vibron coupling strengths of the Fe4 are computed using DFT. A giant spin model is applied to the Fe4 with only two charge states, specifically a neutral state with a total spin S =5 and a singly charged state with S =9 /2 , which is consistent with our DFT result and experiments on Fe4 single-molecule transistors. In sequential electron tunneling, we find that the magnetic anisotropy gives rise to new features in the conductance peaks arising from vibrational excitations. In particular, the peak height shows a strong, unusual dependence on the direction as well as magnitude of applied B field. The magnetic anisotropy also introduces vibrational satellite peaks whose position and height are modified with the direction and magnitude of applied B field. Furthermore, when multiple vibrational modes with considerable electron-vibron coupling have energies close to one another, a low-bias current is suppressed, independently of gate voltage and applied B field, although that is not the case for a single mode with a similar electron-vibron coupling. In the former case, the conductance peaks reveal a stronger B -field dependence than in the latter case. The new features appear because the magnetic anisotropy barrier is of the same order of magnitude as the energies of vibrational modes with significant electron-vibron coupling. Our findings clearly show the interesting interplay between magnetic anisotropy and electron-vibron coupling in electron transport via the Fe4. Similar behavior can be observed in transport via other anisotropic magnetic molecules.

  11. Hot-electron-mediated desorption rates calculated from excited-state potential energy surfaces

    DEFF Research Database (Denmark)

    Olsen, Thomas; Gavnholt, Jeppe; Schiøtz, Jakob

    2009-01-01

    We present a model for desorption induced by (multiple) electronic transitions [DIET (DIMET)] based on potential energy surfaces calculated with the delta self-consistent field extension of density-functional theory. We calculate potential energy surfaces of CO and NO molecules adsorbed on various...... transition-metal surfaces and show that classical nuclear dynamics does not suffice for propagation in the excited state. We present a simple Hamiltonian describing the system with parameters obtained from the excited-state potential energy surface and show that this model can describe desorption dynamics...... in both the DIET and DIMET regimes and reproduce the power-law behavior observed experimentally. We observe that the internal stretch degree of freedom in the molecules is crucial for the energy transfer between the hot electrons and the molecule when the coupling to the surface is strong....

  12. Non-adiabatic rotational excitation of dipolar molecule under the ...

    Indian Academy of Sciences (India)

    NAREX is useful for studies on quantum state resolved collision or reaction dynamics of highly anisotropic state. NAREX can become an important tool for changing and controlling the rotational state distribu- tion of molecules, especially when recent elaborate methods i.e. double-pulse pair28 and shaped pulses29,30.

  13. Catalytic synthesis of ammonia using vibrationally excited nitrogen molecules

    DEFF Research Database (Denmark)

    Hansen, Flemming Yssing; Henriksen, Niels Engholm; Billing, Gert D.

    1992-01-01

    The dissociation of nitrogen is the rate-limiting step in the catalytic synthesis of ammonia. Theoretical calculations have shown that the dissociative sticking probability of molecular nitrogen on catalytic active metal surfaces is enhanced by orders of magnitude when the molecules...

  14. Double-electron excitation above Xe K-edge

    International Nuclear Information System (INIS)

    Ito, Y.; Tochio, T.; Vlaicu, A.M.; Mutaguchi, K.; OhHashi, H.; Shigeoka, N.; Nakata, Y.; Akahama, Y.; Uruga, T.; Emura, Sh.

    2000-01-01

    When X-rays fall on any substance, whether solid, liquid, or gaseous, a photoabsorption occurs. Photoabsorption in atoms has been generally treated as a single-electron excitation process. However, the existence of the multi-electron excitation process, where the removal of a core electron by photoabsorption causes excitation of additional electrons in the same atoms, has been known in x-ray absorption spectra for a long time. In x-ray absorption spectra, experimental investigations of the shake processes in inner-shell ionization phenomena have been performed by detecting discontinuities. The shake effect which is a consequence of rearrangement of the atomic electrons, occurs in association with inner-shell excitation and ionization phenomena in x-ray absorption. The shake process has been studied extensively in various gases, because it is usually considered that the measurement of the multi-electron excitation is only possible for monatomic gases or vapors. The x-ray absorption spectra in Kr gas were measured by Ito et al. in order to observe precisely x-ray absorption spectra and to investigate the multi-electron excitation cross sections in Kr as a function of photon energy using synchrotron radiation. However, no suitable measured K x-ray absorption spectra was available to elucidate the shake processes. In the present work, the photoabsorption cross sections in Xe have been precisely measured in order to determine the features on the shake processes resulting from multiple electron excitations as a function of photon energy. Double-electron transitions of [1s4d], [1s4p], [1s4s], and [1s3d] are first detected. (author)

  15. Extending single molecule fluorescence observation time by amplitude-modulated excitation

    Science.gov (United States)

    Kisley, Lydia; Chang, Wei-Shun; Cooper, David; Mansur, Andrea P.; Landes, Christy F.

    2013-09-01

    We present a hardware-based method that can improve single molecule fluorophore observation time by up to 1500% and super-localization by 47% for the experimental conditions used. The excitation was modulated using an acousto-optic modulator (AOM) synchronized to the data acquisition and inherent data conversion time of the detector. The observation time and precision in super-localization of four commonly used fluorophores were compared under modulated and traditional continuous excitation, including direct total internal reflectance excitation of Alexa 555 and Cy3, non-radiative Förster resonance energy transfer (FRET) excited Cy5, and direct epi-fluorescence wide field excitation of Rhodamine 6G. The proposed amplitude-modulated excitation does not perturb the chemical makeup of the system or sacrifice signal and is compatible with multiple types of fluorophores. Amplitude-modulated excitation has practical applications for any fluorescent study utilizing an instrumental setup with time-delayed detectors.

  16. Extending single molecule fluorescence observation time by amplitude-modulated excitation

    International Nuclear Information System (INIS)

    Kisley, Lydia; Chang, Wei-Shun; Cooper, David; Mansur, Andrea P; Landes, Christy F

    2013-01-01

    We present a hardware-based method that can improve single molecule fluorophore observation time by up to 1500% and super-localization by 47% for the experimental conditions used. The excitation was modulated using an acousto-optic modulator (AOM) synchronized to the data acquisition and inherent data conversion time of the detector. The observation time and precision in super-localization of four commonly used fluorophores were compared under modulated and traditional continuous excitation, including direct total internal reflectance excitation of Alexa 555 and Cy3, non-radiative Förster resonance energy transfer (FRET) excited Cy5, and direct epi-fluorescence wide field excitation of Rhodamine 6G. The proposed amplitude-modulated excitation does not perturb the chemical makeup of the system or sacrifice signal and is compatible with multiple types of fluorophores. Amplitude-modulated excitation has practical applications for any fluorescent study utilizing an instrumental setup with time-delayed detectors. (technical note)

  17. Electron collision data for polyatomic molecules in plasma processing and environmental processes

    International Nuclear Information System (INIS)

    Tanaka, H.; Kitajima, M.; Cho, H.

    2002-01-01

    The experimental studies for electron-polyatomic molecule collision are reviewed in connection with the plasma processing and environmental issues. Recent developments in electron scattering experiments on the differential cross section measurements for various processes such as elastic scattering, vibrational, and electronic excitations are summarized from high to low energy regions (1-100 eV). The need for cross-section data for a broad variety of molecular species is also discussed because there is an urgent need to develop an international program to provide the scientific and technological communities with authoritative cross sections for electron-molecule interactions

  18. Electron-impact excitation of ions

    International Nuclear Information System (INIS)

    Crandall, D.H.

    1981-01-01

    A review of electron-ion beam experiments is given. Techniques, difficulties, and present trends in this area are discussed. Measured cross sections are compared with theoretical results and the current level of agreement is assessed. 74 references

  19. Modeling Electronic-Nuclear Interactions for Excitation Energy Transfer Processes in Light-Harvesting Complexes.

    Science.gov (United States)

    Lee, Mi Kyung; Coker, David F

    2016-08-18

    An accurate approach for computing intermolecular and intrachromophore contributions to spectral densities to describe the electronic-nuclear interactions relevant for modeling excitation energy transfer processes in light harvesting systems is presented. The approach is based on molecular dynamics (MD) calculations of classical correlation functions of long-range contributions to excitation energy fluctuations and a separate harmonic analysis and single-point gradient quantum calculations for electron-intrachromophore vibrational couplings. A simple model is also presented that enables detailed analysis of the shortcomings of standard MD-based excitation energy fluctuation correlation function approaches. The method introduced here avoids these problems, and its reliability is demonstrated in accurate predictions for bacteriochlorophyll molecules in the Fenna-Matthews-Olson pigment-protein complex, where excellent agreement with experimental spectral densities is found. This efficient approach can provide instantaneous spectral densities for treating the influence of fluctuations in environmental dissipation on fast electronic relaxation.

  20. Dissociative Excitation of Acetylene Induced by Electron Impact: Excitation-emission Cross-sections

    Energy Technology Data Exchange (ETDEWEB)

    Országh, Juraj; Danko, Marián; Čechvala, Peter; Matejčík, Štefan, E-mail: matejcik@fmph.uniba.sk [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Mlynská dolina F-2, 842 48 Bratislava (Slovakia)

    2017-05-20

    The optical emission spectrum of acetylene excited by monoenergetic electrons was studied in the range of 190–660 nm. The dissociative excitation and dissociative ionization associated with excitation of the ions initiated by electron impact were dominant processes contributing to the spectrum. The spectrum was dominated by the atomic lines (hydrogen Balmer series, carbon) and molecular bands (CH(A–X), CH(B–X), CH{sup +}(B–A), and C{sub 2}). Besides the discrete transitions, we have detected the continuum emission radiation of ethynyl radical C{sub 2}H(A–X). For most important lines and bands of the spectrum we have measured absolute excitation-emission cross sections and determined the energy thresholds of the particular dissociative channels.

  1. Ultrafast electron diffraction studies of optically excited thin bismuth films

    International Nuclear Information System (INIS)

    Rajkovic, Ivan

    2008-01-01

    This thesis contains work on the design and the realization of an experimental setup capable of providing sub-picosecond electron pulses for ultrafast electron diffraction experiments, and performing the study of ultrafast dynamics in bismuth after optical excitation using this setup. (orig.)

  2. Excited electronic state decomposition mechanisms of clusters of ...

    Indian Academy of Sciences (India)

    In this report, electronically non-adiabatic decomposition pathways of clusters of dimethylnitramine and aluminum (DMNA-Al and DMNA-Al2) are discussed in comparison to isolated dimethylnitramine (DMNA). Electronically excited state processes of DMNA-Al and DMNA-Al2 are explored using the complete active space ...

  3. Ultrafast electron diffraction studies of optically excited thin bismuth films

    Energy Technology Data Exchange (ETDEWEB)

    Rajkovic, Ivan

    2008-10-21

    This thesis contains work on the design and the realization of an experimental setup capable of providing sub-picosecond electron pulses for ultrafast electron diffraction experiments, and performing the study of ultrafast dynamics in bismuth after optical excitation using this setup. (orig.)

  4. Rotational excitation of interstellar molecular ions by electrons

    Energy Technology Data Exchange (ETDEWEB)

    Faure, A [Laboratoire d' Astrophysique, UMR 5571 CNRS, Universite Joseph-Fourier, B.P. 53, 38041 Grenoble cedex 09 (France); Tennyson, J [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Kokoouline, V [Department of Physics, University of Central Florida, Orlando, Florida 32816 (United States); Greene, Chris H, E-mail: afaure@obs.ujf-grenoble.f [Department of Physics and JILA, University of Colorado, Boulder, Colorado 80309-0440 (United States)

    2009-11-15

    Electrons are known to be efficient in rotationally exciting molecular ions in cold ionized media. Rotational effects have also been shown to affect the dissociative recombination (DR) process. Electron collisions are thus expected to play a significant role in the thermalization and dissociation dynamics of molecular ions, both in the laboratory and in space. Using the molecular R-matrix method combined with the Adiabatic-Nuclei-Rotation (ANR) approximation corrected for threshold and closed-channel effects, we have computed new rate coefficients for the rotational excitation of H{sup +}{sub 3} and HCO{sup +} by electrons at temperatures from 10 to 1 000K. At temperatures above rotational thresholds, rotational rates are found to compete or even dominate those of dissociative recombination, suggesting that electron collisions provide a possible source of rotational (de)excitation in DR measurements.

  5. Ab Initio molecular dynamics with excited electrons

    NARCIS (Netherlands)

    Alavi, A.; Kohanoff, J.; Parrinello, M.; Frenkel, D.

    1994-01-01

    A method to do ab initio molecular dynamics suitable for metallic and electronically hot systems is described. It is based on a density functional which is costationary with the finite-temperature functional of Mermin, with state being included with possibly fractional occupation numbers.

  6. Molecular electronics: the single molecule switch and transistor

    NARCIS (Netherlands)

    Sotthewes, Kai; Geskin, Victor; Heimbuch, Rene; Kumar, Avijit; Zandvliet, Henricus J.W.

    2014-01-01

    In order to design and realize single-molecule devices it is essential to have a good understanding of the properties of an individual molecule. For electronic applications, the most important property of a molecule is its conductance. Here we show how a single octanethiol molecule can be connected

  7. Excitation two-center interference and the orbital geometry in laser-induced nonsequential double ionization of diatomic molecules

    International Nuclear Information System (INIS)

    Shaaran, T.; Augstein, B. B.; Figueira de Morisson Faria, C.

    2011-01-01

    We address the influence of the molecular orbital geometry and of the molecular alignment with respect to the laser-field polarization on laser-induced nonsequential double ionization of diatomic molecules for different molecular species, namely N 2 and Li 2 . We focus on the recollision excitation with subsequent tunneling ionization (RESI) mechanism, in which the first electron, upon return, promotes the second electron to an excited state, from where it subsequently tunnels. We assume that both electrons are initially in the highest occupied molecular orbital (HOMO) and that the second electron is excited to the lowest unoccupied molecular orbital (LUMO). We show that the electron-momentum distributions exhibit interference maxima and minima due to the electron emission at spatially separated centers. We provide generalized analytical expressions for such maxima or minima, which take into account s-p mixing and the orbital geometry. The patterns caused by the two-center interference are sharpest for vanishing alignment angle and get washed out as this parameter increases. Apart from that, there exist features due to the geometry of the LUMO, which may be observed for a wide range of alignment angles. Such features manifest themselves as the suppression of probability density in specific momentum regions due to the shape of the LUMO wave function, or as an overall decrease in the RESI yield due to the presence of nodal planes.

  8. Coherence in electron-impact excitation of helium

    International Nuclear Information System (INIS)

    Batelaan, Hermanus.

    1991-01-01

    This thesis describes an experimental study into the electron-impact excitation to the 3 3 P, 3 1 D and 3 3 D states of Helium. The scattered electron and the photon, emitted by the excited atom, are measured in coincidence. The parameters, which can be varied, are the scattering angle and the kinetic energy of the projectile. Two parameters, which are used to characterize the excited state, are the angular momentum transferred to the atom, L perpendicular, and the alignment angle γ. It is shown that results of measurements on 3 1 D excitation with photon detection perpendicular to the scattering plane do not agree in the small scattering angle region with any of the model calculations currently available. Remarkable is the sign of L perpendicular, which appears to start of negatively at 60 eV. It is shown that for 3 3 P excitation the predicted large value of γ is indeed found experimentally. This supports the suggestion that exchange scattering is underestimated in model calculations for 1 P excitation. Another result is that for 1 P and 3 P excitation the behaviour of L perpendicular as a function of the scattering angle can be related at different impact energies with the help of a partial wave expansion. A scaling relation can be formulated for the behaviour of L perpendicular. The influence of a negative ion resonance to excitation of the 3 3 D state is investigated. Both in coincidence and non-coincidence measurements the presence of the resonance yields information on both the direct and indirect excitation of the 3 3 D state. It is shown that the coincident measurement gives an unique opportunity to determine the excited 3 3 D state completely. Results of measurements with photon detection in the scattering plane are given. They supplement previous 3 1 D and 3 3 D results and allow physical parameters, such as L perpendicular and γ, to be obtained. (H.W.). 132 refs.; 20 figs.; 18 tabs

  9. Extremely confined gap surface-plasmon modes excited by electrons

    DEFF Research Database (Denmark)

    Raza, Søren; Stenger, Nicolas; Pors, Anders Lambertus

    2014-01-01

    EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to ~5...... nm. We argue that excitation of this mode, featuring very strong absorption, has a crucial role in experimental realizations of non-resonant light absorption by ultra-sharp convex grooves with fabrication-induced asymmetry. The occurrence of the antisymmetric GSP mode along with the fundamental GSP...

  10. Vibrational energy transfer in selectively excited diatomic molecules

    International Nuclear Information System (INIS)

    Dasch, C.J.

    1978-09-01

    Single rovibrational states of HCl(v=2), HBr(v=2), DCl(v=2), and CO(v=2) were excited with a pulsed optical parametric oscillator (OPO). Total vibrational relaxation rates near - resonance quenchers were measured at 295 0 K using time resolved infrared fluorescence. These rates are attributed primarily to V - V energy transfer, and they generally conform to a simple energy gap law. A small deviation was found for the CO(v) + DCl(v') relaxation rates. Upper limits for the self relaxation by V - R,T of HCl(v=2) and HBr(v=2) and for the two quantum exchange between HCl and HBr were determined. The HF dimer was detected at 295 0 K and 30 torr HF pressure with an optoacoustic spectrometer using the OPO. Pulsed and chopped, resonant and non-resonant spectrophones are analyzed in detail. From experiments and first order perturbation theory, these V - V exchange rates appear to behave as a first order perturbation in the vibrational coordinates. The rotational dynamics are known to be complicated however, and the coupled rotational - vibrational dynamics were investigated theoreticaly in infinite order by the Dillon and Stephenson and the first Magnus approximations. Large ΔJ transitions appear to be important, but these calculations differ by orders of magnitude on specific rovibrational transition rates. Integration of the time dependent semiclassical equations by a modified Gordon method and a rotationally distorted wave approximation are discussed as methods which would treat the rotational motion more accurately. 225 references

  11. Electron transport through a diatomic molecule

    Energy Technology Data Exchange (ETDEWEB)

    Imran, Muhammad, E-mail: imran1gee@gmail.com

    2014-08-01

    Electron transport through a diatomic molecular tunnel junction shows wave like interference phenomenon. By using Keldysh non-equilibrium Green's function (NEGF) theory, we have explicitly presented current and differential conductance calculation for a diatomic molecular and two isolated atoms (two atoms having zero hybridization between their energy orbitals) tunnel junctions. In case of a diatomic molecular tunnel junction, Green's function propagators entering into current and differential conductance formula interfere constructively for a molecular anti-bonding state and destructively for bonding state. Consequently, conductance through a molecular bonding state is suppressed, and to conserve current, conductance through anti-bonding state is enhanced. Therefore, current steps and differential conductance peaks amplitude show asymmetric correspondence between molecular bonding and anti-bonding states. Interestingly, for a diatomic molecule, comprising of two atoms of same energy level, these propagators interfere completely destructively for molecular bonding state and constructively for molecular anti-bonding state. Hence under such condition, a single step or a single peak is shown up in current versus voltage or differential conductance versus voltage studies.

  12. Electron transport through a diatomic molecule

    International Nuclear Information System (INIS)

    Imran, Muhammad

    2014-01-01

    Electron transport through a diatomic molecular tunnel junction shows wave like interference phenomenon. By using Keldysh non-equilibrium Green's function (NEGF) theory, we have explicitly presented current and differential conductance calculation for a diatomic molecular and two isolated atoms (two atoms having zero hybridization between their energy orbitals) tunnel junctions. In case of a diatomic molecular tunnel junction, Green's function propagators entering into current and differential conductance formula interfere constructively for a molecular anti-bonding state and destructively for bonding state. Consequently, conductance through a molecular bonding state is suppressed, and to conserve current, conductance through anti-bonding state is enhanced. Therefore, current steps and differential conductance peaks amplitude show asymmetric correspondence between molecular bonding and anti-bonding states. Interestingly, for a diatomic molecule, comprising of two atoms of same energy level, these propagators interfere completely destructively for molecular bonding state and constructively for molecular anti-bonding state. Hence under such condition, a single step or a single peak is shown up in current versus voltage or differential conductance versus voltage studies.

  13. Quantum control of molecular vibrational and rotational excitations in a homonuclear diatomic molecule: A full three-dimensional treatment with polarization forces

    Science.gov (United States)

    Ren, Qinghua; Balint-Kurti, Gabriel G.; Manby, Frederick R.; Artamonov, Maxim; Ho, Tak-San; Rabitz, Herschel

    2006-01-01

    The optimal control of the vibrational excitation of the hydrogen molecule [Balint-Kurti et al., J. Chem. Phys. 122, 084110 (2005)] utilizing polarization forces is extended to three dimensions. The polarizability of the molecule, to first and higher orders, is accounted for using explicit ab initio calculations of the molecular electronic energy in the presence of an electric field. Optimal control theory is then used to design infrared laser pulses that selectively excite the molecule to preselected vibrational-rotational states. The amplitude of the electric field of the optimized pulses is restricted so that there is no significant ionization during the process, and a new frequency sifting method is used to simplify the frequency spectrum of the pulse. The frequency spectra of the optimized laser pulses for processes involving rotational excitation are more complex than those relating to processes involving only vibrational excitation.

  14. Intermediate energy electron impact excitation of composite vibrational modes in phenol

    Energy Technology Data Exchange (ETDEWEB)

    Neves, R. F. C. [School of Chemical and Physical Sciences, Flinders University, G.P.O. Box 2100, Adelaide, SA 5001 (Australia); Instituto Federal do Sul de Minas Gerais, Campus Poços de Caldas, Minas Gerais (Brazil); Departamento de Física, Universidade Federal de Juiz de Fora, 36036-900, Juiz de Fora, Minas Gerais (Brazil); Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, G.P.O. Box 2100, Adelaide, SA 5001 (Australia); Lopes, M. C. A.; Nixon, K. L. [Departamento de Física, Universidade Federal de Juiz de Fora, 36036-900, Juiz de Fora, Minas Gerais (Brazil); Oliveira, E. M. de; Lima, M. A. P. [Instituto de Física ‘Gleb Wataghin,’ Universidade Estadual de Campinas, 13083-859 Campinas, São Paulo (Brazil); Costa, R. F. da [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-580 Santo André, São Paulo (Brazil); Varella, M. T. do N. [Instituto de Física, Universidade de São Paulo, C.P. 66318, 05315-970 São Paulo (Brazil); Bettega, M. H. F. [Departamento de Física, Universidade Federal do Paraná, C.P. 19044, 81531-990 Curitiba, Paraná (Brazil); Silva, G. B. da [Universidade Federal de Mato Grosso, Barra do Garças, Mato Grosso (Brazil); Brunger, M. J., E-mail: Michael.Brunger@flinders.edu.au [School of Chemical and Physical Sciences, Flinders University, G.P.O. Box 2100, Adelaide, SA 5001 (Australia); Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2015-05-21

    We report differential cross section results from an experimental investigation into the electron impact excitation of a number of the low-lying composite (unresolved) vibrational modes in phenol (C{sub 6}H{sub 5}OH). The measurements were carried out at incident electron energies in the range 15–40 eV and for scattered-electron angles in the range 10–90°. The energy resolution of those measurements was typically ∼80 meV. Calculations, using the GAMESS code, were also undertaken with a B3LYP/aug-cc-pVDZ level model chemistry, in order to enable us to assign vibrational modes to the features observed in our energy loss spectra. To the best of our knowledge, the present cross sections are the first to be reported for vibrational excitation of the C{sub 6}H{sub 5}OH molecule by electron impact.

  15. Study on infrared multiphoton excitation of the linear triatomic molecule by the Lie-algebra approach

    International Nuclear Information System (INIS)

    Feng, H.; Zheng, Y.; Ding, S.

    2007-01-01

    Infrared multiphoton vibrational excitation of the linear triatomic molecule has been studied using the quadratic anharmonic Lie-algebra model, unitary transformations, and Magnus approximation. An explicit Lie-algebra expression for the vibrational transition probability is obtained by using a Lie-algebra approach. This explicit Lie-algebra expressions for time-evolution operator and vibrational transition probabilities make the computation clearer and easier. The infrared multiphoton vibrational excitation of the DCN linear tri-atomic molecule is discussed as an example

  16. Spectroscopic Diagnosis of Excited-State Aromaticity: Capturing Electronic Structures and Conformations upon Aromaticity Reversal.

    Science.gov (United States)

    Oh, Juwon; Sung, Young Mo; Hong, Yongseok; Kim, Dongho

    2018-03-06

    Aromaticity, the special energetic stability derived from cyclic [4 n + 2]π-conjugated electronic structures, has been the topic of intense interest in chemistry because it plays a critical role in rationalizing molecular stability, reactivity, and physical/chemical properties. Recently, the pioneering work by Colin Baird on aromaticity reversal, postulating that aromatic (antiaromatic) character in the ground state reverses to antiaromatic (aromatic) character in the lowest excited triplet state, has attracted much scientific attention. The completely reversed aromaticity in the excited state provides direct insight into understanding the photophysical/chemical properties of photoactive materials. In turn, the application of aromatic molecules to photoactive materials has led to numerous studies revealing this aromaticity reversal. However, most studies of excited-state aromaticity have been based on the theoretical point of view. The experimental evaluation of aromaticity in the excited state is still challenging and strenuous because the assessment of (anti)aromaticity with conventional magnetic, energetic, and geometric indices is difficult in the excited state, which practically restricts the extension and application of the concept of excited-state aromaticity. Time-resolved optical spectroscopies can provide a new and alternative avenue to evaluate excited-state aromaticity experimentally while observing changes in the molecular features in the excited states. Time-resolved optical spectroscopies take advantage of ultrafast laser pulses to achieve high time resolution, making them suitable for monitoring ultrafast changes in the excited states of molecular systems. This can provide valuable information for understanding the aromaticity reversal. This Account presents recent breakthroughs in the experimental assessment of excited-state aromaticity and the verification of aromaticity reversal with time-resolved optical spectroscopic measurements. To

  17. Calculation of electron impact inelastic cross sections and rate coefficients for diatomic molecules. Application to air molecules

    International Nuclear Information System (INIS)

    Teulet, P.; Sarrette, J.P.; Gomes, A.M.

    1999-01-01

    A method based upon the modified Weighted Total Cross Section (WTCS) theory for the determination of electron impact excitation, ionization and dissociation cross sections and rate coefficients is proposed. An application to the main electronic states of diatomic molecules of the air (O 2 , N 2 and NO) and the corresponding ions (O + 2 , N + 2 and NO + ) is given. The reaction rate coefficients were calculated using one and two kinetic temperatures (θ e and θ g for electrons and heavy particles, respectively) and were fitted in the Arrhenius form in the range 1500-15andpuncsp; omitted000 K. This method can be easily extended to any diatomic molecule. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  18. Studies of photoionization processes from ground-state and excited-state atoms and molecules

    International Nuclear Information System (INIS)

    Ederer, D.L.; Parr, A.C.; West, J.B.

    1982-01-01

    Recent triply-differential photoelectron spectroscopy experiments designed for the study of correlation effects in atoms and molecules are described. Final-state symmetry of the n=2 state of helium has been determined. The non-Franck-Condon behavior of vibrational branching ratios and large variations of the angular asymmetry parameter has been observed for shape resonances and autoionizing resonances in CO and other molecules. Recent observations of the photoionization of excited sodium atoms are also described

  19. General active space commutator-based coupled cluster theory of general excitation rank for electronically excited states: implementation and application to ScH.

    Science.gov (United States)

    Hubert, Mickaël; Olsen, Jeppe; Loras, Jessica; Fleig, Timo

    2013-11-21

    We present a new implementation of general excitation rank coupled cluster theory for electronically excited states based on the single-reference multi-reference formalism. The method may include active-space selected and/or general higher excitations by means of the general active space concept. It may employ molecular integrals over the four-component Lévy-Leblond Hamiltonian or the relativistic spin-orbit-free four-component Hamiltonian of Dyall. In an initial application to ground- and excited states of the scandium monohydride molecule we report spectroscopic constants using basis sets of up to quadruple-zeta quality and up to full iterative triple excitations in the cluster operators. Effects due to spin-orbit interaction are evaluated using two-component multi-reference configuration interaction for assessing the accuracy of the coupled cluster results.

  20. Excited electronic state decomposition mechanisms of clusters of ...

    Indian Academy of Sciences (India)

    Excited electronic state decomposition mechanisms of clusters of dimethylnitramine and aluminum. ANUPAM BERA and ATANU BHATTACHARYA. ∗. Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India e-mail: atanub@ipc.iisc.ernet.in. MS received 5 September 2014; ...

  1. 23P excitation of helium by electron impact

    International Nuclear Information System (INIS)

    Roeder, J.; Ehrhardt, H.; Bray, I.; Fursa, D.

    1996-03-01

    We present highly accurate relative measurements of 23P excitation of helium by electron impact at 30, 40 and 50 eV. These, when normalised to the convergent close-coupling (CCC) theory at one angle, yield excellent agreement at the remaining angles. This resolves some of the outstanding discrepancies between the CCC theory and earlier measurements. (authors). 14 refs., 3 figs

  2. Vibrational excitation and vibrationally resolved electronic excitation cross sections of positron-H2 scattering

    Science.gov (United States)

    Zammit, Mark; Fursa, Dmitry; Savage, Jeremy; Bray, Igor

    2016-09-01

    Vibrational excitation and vibrationally resolved electronic excitation cross sections of positron-H2 scattering have been calculated using the single-centre molecular convergent close-coupling (CCC) method. The adiabatic-nuclei approximation was utilized to model the above scattering processes and obtain the vibrationally resolved positron-H2 scattering length. As previously demonstrated, the CCC results are converged and accurately account for virtual and physical positronium formation by coupling basis functions with large orbital angular momentum. Here vibrationally resolved integrated and differential cross sections are presented over a wide energy range and compared with previous calculations and available experiments. Los Alamos National Laboratory and Curtin University.

  3. Quantum resonance, Anderson localisation and selective rotational excitation in periodically kicked molecules

    Directory of Open Access Journals (Sweden)

    Averbukh I. Sh.

    2013-03-01

    Full Text Available We show that molecules kicked periodically by laser pulses currently used in molecular alignment experiments allow to observe effects of the periodically kicked quantum rotor in a real rotational system. Among these effects are Anderson localisation in angular momentum and the scaling of the quantum resonance. Based on this, we propose a new scheme for selective molecular rotational excitation.

  4. Excitation of vibrational quanta in furfural by intermediate-energy electrons

    Energy Technology Data Exchange (ETDEWEB)

    Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Neves, R. F. C. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Instituto Federal do Sul de Minas Gerais, Campus Poços de Caldas, Minas Gerais (Brazil); Departamento de Física, Universidade Federal de Juiz de Fora, 36036-900, Juiz de Fora, MG (Brazil); Lopes, M. C. A. [Departamento de Física, Universidade Federal de Juiz de Fora, 36036-900, Juiz de Fora, MG (Brazil); Costa, R. F. da [Instituto de Física “Gleb Wataghin,” Universidade Estadual de Campinas, Campinas, 13083-859 São Paulo (Brazil); Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, 09210-580 São Paulo (Brazil); Varella, M. T. do N. [Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970 São Paulo, São Paulo (Brazil); Bettega, M. H. F. [Departamento de Física, Universidade Federal do Paraná, CP 19044, 81531-990 Curitiba, Paraná (Brazil); Lima, M. A. P. [Instituto de Física “Gleb Wataghin,” Universidade Estadual de Campinas, Campinas, 13083-859 São Paulo (Brazil); García, G. [Instituto de Física Fundamental, CSIC, Serrano 113-bis, 28006 Madrid (Spain); and others

    2015-12-14

    We report cross sections for electron-impact excitation of vibrational quanta in furfural, at intermediate incident electron energies (20, 30, and 40 eV). The present differential cross sections are measured over the scattered electron angular range 10°–90°, with corresponding integral cross sections subsequently being determined. Furfural is a viable plant-derived alternative to petrochemicals, being produced via low-temperature plasma treatment of biomass. Current yields, however, need to be significantly improved, possibly through modelling, with the present cross sections being an important component of such simulations. To the best of our knowledge, there are no other cross sections for vibrational excitation of furfural available in the literature, so the present data are valuable for this important molecule.

  5. Electron-impact excitation and ionization cross sections for ground state and excited helium atoms

    International Nuclear Information System (INIS)

    Ralchenko, Yu.; Janev, R.K.; Kato, T.; Fursa, D.V.; Bray, I.; Heer, F.J. de

    2008-01-01

    Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n≤4 are treated individually, while the states with n≥5 are considered degenerate. For the processes involving transitions to and from n≥5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form

  6. Ultrafast Imaging of Electronic Motion in Atoms and Molecules

    Science.gov (United States)

    2016-01-12

    AFRL-AFOSR-VA-TR-2016-0045 Ultrafast Imaging of Electronic Motion in Atoms and Molecules Martin Centurion UNIVERSITY OF NEBRSKA Final Report 01/12...Ultrafast Imaging of Electronic Motion in Atoms and Molecules 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-12-1-0149 5c. PROGRAM ELEMENT NUMBER 6...a gaseous target of atoms or molecules. An optical setup was designed and constructed to compensate for the blurring of the temporal resolution due

  7. Electron emission from materials at low excitation energies

    International Nuclear Information System (INIS)

    Urma, N.; Kijek, M.; Millar, J.J.

    1996-01-01

    Full text: An experimental system has been designed and developed with the purpose of measuring the total electron emission yield from materials at low energy excitation. In the first instance the reliability of the system was checked by measuring the total electron emission yield for a well defined surface (aluminium 99.45%). The obtained data was in the expected range given by the literature, and consequently the system will be used further for measuring the total electron yield for a range of materials with interest in the instrumentation industry. We intend to measure the total electron emission yield under electron bombardment as a function of incident electron energy up to 1200 eV, angle of incidence, state of the surface and environment to which the surface has been exposed. Dependence of emission on total electron irradiated dose is also of interest. For many practical application of the 'Secondary Electron Emission', the total electron yield is desired to be as large as possible. The above phenomenon has practical applicability in electron multiplier tube and Scanning electron microscopy - when by means of the variation of the yield of the emitted electrons one may produce visible images of small sample areas. The electron multiplier tube, is a device which utilises the above effect to detect and amplify both single particles and low currents streams of charged particles. The majority of electron tubes use electrons with low energy, hundreds of eV. Not a lot has been published in the literature about this regime and also about the emission when the impinging electrons have small energy, up to 1 KeV. The information obtained from the experimental measurements concerning the total electron emission yield is used to asses the investigated materials as a potential electron emitting surfaces or dynodes in an electron multiplier tube

  8. Dynamics of two-electron excitations in helium

    Energy Technology Data Exchange (ETDEWEB)

    Caldwell, C.D.; Menzel, A.; Frigo, S.P. [Univ. of Central Florida, Orlando, FL (United States)] [and others

    1997-04-01

    Excitation of both electrons in helium offers a unique window for studying electron correlation at the most basic level in an atom in which these two electrons and the nucleus form a three-body system. The authors utilized the first light available at the U-8 undulator-SGM monochromator beamline to investigate the dynamic parameters, partial cross sections, differential cross sections, and photoelectron angular distribution parameters ({beta}), with a high resolving power for the photon beam and at the highly differential level afforded by the use of their electron spectrometer. In parallel, they carried out detailed calculations of the relevant properties by a theoretical approach that is based on the hyperspherical close-coupling method. Partial photoionization cross sections {sigma}{sub n}, and photoelectron angular distributions {beta}{sub n} were measured for all possible final ionic states He{sup +}(n) in the region of the double excitations N(K,T){sup A} up to the N=5 threshold. At a photon energy bandpass of 12 meV below the thresholds N=3, 4, and 5, this level of differentiation offers the most critical assessment of the dynamics of the two-electron excitations to date. The experimental data were seen to be very well described by the most advanced theoretical calculations.

  9. Chemical modulation of electronic structure at the excited state

    Science.gov (United States)

    Li, F.; Song, C.; Gu, Y. D.; Saleem, M. S.; Pan, F.

    2017-12-01

    Spin-polarized electronic structures are the cornerstone of spintronics, and have thus attracted a significant amount of interest; in particular, researchers are looking into how to modulate the electronic structure to enable multifunctional spintronics applications, especially in half-metallic systems. However, the control of the spin polarization has only been predicted in limited two-dimensional systems with spin-polarized Dirac structures and is difficult to achieve experimentally. Here, we report the modulation of the electronic structure in the light-induced excited state in a typical half-metal, L a1 /2S r1 /2Mn O3 -δ . According to the spin-transport measurements, there appears a light-induced increase in magnetoresistance due to the enhanced spin scattering, which is closely associated with the excited spin polarization. Strikingly, the light-induced variation can be enhanced via alcohol processing and reduced by oxygen annealing. X-ray photoelectron spectroscopy measurements show that in the chemical process, a redox reaction occurs with a change in the valence of Mn. Furthermore, first-principles calculations reveal that the change in the valence of Mn alters the electronic structure and consequently modulates the spin polarization in the excited state. Our findings thus report a chemically tunable electronic structure, demonstrating interesting physics and the potential for multifunctional applications and ultrafast spintronics.

  10. Redox-gated electron transport in electrically wired ferrocene molecules

    Energy Technology Data Exchange (ETDEWEB)

    Xiao Xiaoyin [Department of Electrical Engineering and Center for Solid State Electronic Research, Arizona State University, Tempe, AZ 85287 (United States); Brune, Daniel [Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287 (United States); He Jin [Center for Single Molecule Biophysics, Biodesign Institute, Arizona State University, Tempe, AZ 85287 (United States); Lindsay, Stuart [Center for Single Molecule Biophysics, Biodesign Institute, Arizona State University, Tempe, AZ 85287 (United States); Gorman, Christopher B. [Department of Chemistry, North Carolina State University, Raleigh, NC 27695-8204 (United States); Tao Nongjian [Department of Electrical Engineering and Center for Solid State Electronic Research, Arizona State University, Tempe, AZ 85287 (United States)], E-mail: nongjian.tao@asu.edu

    2006-07-11

    We have synthesized cysteamine-terminated ferrocene molecules and determined the dependence of the electron transport properties of the molecules on their redox states by measuring the current through the molecules as a function of the electrode potential. The current fluctuates over a large range, but its average value increases with the potential. We attribute the current fluctuation and its increase with the potential to the switching of the molecules from low-conductance reduced state to high-conductance oxidized state.

  11. Redox-gated electron transport in electrically wired ferrocene molecules

    International Nuclear Information System (INIS)

    Xiao Xiaoyin; Brune, Daniel; He Jin; Lindsay, Stuart; Gorman, Christopher B.; Tao Nongjian

    2006-01-01

    We have synthesized cysteamine-terminated ferrocene molecules and determined the dependence of the electron transport properties of the molecules on their redox states by measuring the current through the molecules as a function of the electrode potential. The current fluctuates over a large range, but its average value increases with the potential. We attribute the current fluctuation and its increase with the potential to the switching of the molecules from low-conductance reduced state to high-conductance oxidized state

  12. Semiclassical study of the collision of a highly excited Rydberg atom with the molecules HF and HCl

    International Nuclear Information System (INIS)

    Kimura, M.; Lane, N.F.

    1990-01-01

    The semiclassical impact-parameter method is applied to the processes of state changing and energy transfer in the collision of a highly excited Rydberg atom (n≥20) with the polar molecules HF and HCl. The relative motion of the molecule and atomic nucleus is taken to be rectilinear; the electron-molecule and ion core-molecule interactions are represented by cutoff dipole forms. Cross sections for transitions involving quantum numbers n and l of the atom and rotational quantum number j of the molecule are obtained for a range of collision energies and initial atomic and molecular states. Comparisons are made with the results of earlier classical studies and with the quantum-mechanical impulse approximation. Collision rates are calculated and compared with experimental values for l mixing and n and j changing. The agreement between experiment and theory is shown to be satisfactory, within the uncertainties of both the measurements and the theory. Cases of agreement and disagreement between various theories are examined. One finding of the present work is that the quantum-mechanical impulse approximation appears to significantly overestimate the values of various state-changing cross sections when the internal energy defect is small. The validity of the impulse approximation for collisions of Rydberg atoms with polar molecules is discussed

  13. Chemical excitation of electrons: A dark path to melanoma.

    Science.gov (United States)

    Premi, Sanjay; Brash, Douglas E

    2016-08-01

    Sunlight's ultraviolet wavelengths induce cyclobutane pyrimidine dimers (CPDs), which then cause mutations that lead to melanoma or to cancers of skin keratinocytes. In pigmented melanocytes, we found that CPDs arise both instantaneously and for hours after UV exposure ends. Remarkably, the CPDs arising in the dark originate by a novel pathway that resembles bioluminescence but does not end in light: First, UV activates the enzymes nitric oxide synthase (NOS) and NADPH oxidase (NOX), which generate the radicals nitric oxide (NO) and superoxide (O2(-)); these combine to form the powerful oxidant peroxynitrite (ONOO(-)). A fragment of the skin pigment melanin is then oxidized, exciting an electron to an energy level so high that it is rarely seen in biology. This process of chemically exciting electrons, termed "chemiexcitation", is used by fireflies to generate light but it had never been seen in mammalian cells. In melanocytes, the energy transfers radiationlessly to DNA, inducing CPDs. Chemiexcitation is a new source of genome instability, and it calls attention to endogenous mechanisms of genome maintenance that prevent electronic excitation or dissipate the energy of excited states. Chemiexcitation may also trigger pathogenesis in internal tissues because the same chemistry should arise wherever superoxide and nitric oxide arise near cells that contain melanin. Copyright © 2016 Elsevier B.V. All rights reserved.

  14. Electron collisions and internal excitation in stored molecular ion beams

    Energy Technology Data Exchange (ETDEWEB)

    Buhr, H.

    2006-07-26

    In storage ring experiments the role, which the initial internal excitation of a molecular ion can play in electron collisions, and the effect of these collisions on the internal excitation are investigated. Dissociative recombination (DR) and inelastic and super-elastic collisions are studied in the system of He{sup +}{sub 2}. The DR rate coefficient at low energies depends strongly on the initial vibrational excitation in this system. Therefore changes in the DR rate coefficient are a very sensitive probe for changes in the vibrational excitation in He{sup +}{sub 2}, which is used to investigate the effects of collisions with electrons and residual gas species. The low-energy DR of HD{sup +} is rich with resonances from the indirect DR process, when certain initial rotational levels in the molecular ion are coupled to levels in neutral Rydberg states lying below the ion state. Using new procedures for high-resolution electron-ion collision spectroscopy developed here, these resonances in the DR cross section can be measured with high energy sensitivity. This allows a detailed comparison with results of a MQDT calculation in an effort to assign some or all of the resonances to certain intermediate Rydberg levels. (orig.)

  15. Electronic structure of molecular Rydberg states of some small molecules and molecular ion

    International Nuclear Information System (INIS)

    Sun Biao; Li Jiaming

    1993-01-01

    Based on an independent-particle-approximation (i.e. the multiple scattering self-consistent-field theory), the electronic structures of Rydberg states of the small diatomic molecules H 2 , He 2 and the He 2 + molecular ion were studied. The principal quantum number of the first state of the Rydberg series is determined from a convention of the limit of the molecular electronic configuration. The dynamics of the excited molecules and molecular ion has been elucidated. The theoretical results are in fair agreement with the existing experimental measurements, thus they can serve as a reliable basis for future refined treatment such as the configuration interaction calculation

  16. Electron impact excitation of atomic hydrogen and hydrogenic ions

    International Nuclear Information System (INIS)

    Bransden, B.H.; Noble, C.J.

    1975-12-01

    The second-order potential model of Bransden and Coleman is used to calculate total cross-sections for the excitation of the n = 2 levels of one-electron ions in the energy interval 25Z 2 to 250Z 2 eV, enabling the range of validity of the Coulomb-Born approximation to be assessed. Previously reported work on the excitation of hydrogen is corrected and extended by the inclusion of exchange effects. Good agreement is obtained with the available experimental data. (author)

  17. Phase coexistence in gallium nanoparticles controlled by electron excitation.

    Science.gov (United States)

    Pochon, S; MacDonald, K F; Knize, R J; Zheludev, N I

    2004-04-09

    In gallium nanoparticles 100 nm in diameter grown on the tip of an optical fiber from an atomic beam we observed equilibrium coexistence of gamma, beta, and liquid structural phases that can be controlled by e-beam excitation in a highly reversible and reproducible fashion. With 2 keV electrons only 1 pJ of excitation energy per nanoparticle is needed to exercise control, with the equilibrium phase achieved in less than a few tenths of a microsecond. The transformations between coexisting phases are accompanied by a continuous change in the nanoparticle film's reflectivity.

  18. DNA-Based Single-Molecule Electronics: From Concept to Function

    Science.gov (United States)

    2018-01-01

    Beyond being the repository of genetic information, DNA is playing an increasingly important role as a building block for molecular electronics. Its inherent structural and molecular recognition properties render it a leading candidate for molecular electronics applications. The structural stability, diversity and programmability of DNA provide overwhelming freedom for the design and fabrication of molecular-scale devices. In the past two decades DNA has therefore attracted inordinate amounts of attention in molecular electronics. This review gives a brief survey of recent experimental progress in DNA-based single-molecule electronics with special focus on single-molecule conductance and I–V characteristics of individual DNA molecules. Existing challenges and exciting future opportunities are also discussed. PMID:29342091

  19. Imaging femtosecond laser-induced electronic excitation in glass

    International Nuclear Information System (INIS)

    Mao Xianglei; Mao, Samuel S.; Russo, Richard E.

    2003-01-01

    While substantial progress has been achieved in understanding laser ablation on the nanosecond and picosecond time scales, it remains a considerable challenge to elucidate the underlying mechanisms during femtosecond laser material interactions. We present experimental observations of electronic excitation inside a wide band gap glass during single femtosecond laser pulse (100 fs, 800 nm) irradiation. Using a femtosecond time-resolved imaging technique, we measured the evolution of a laser-induced electronic plasma inside the glass and calculated the electron number density to be on the order of 10 19 cm -3

  20. Challenges for single molecule electronic devices with nanographene and organic molecules. Do single molecules offer potential as elements of electronic devices in the next generation?

    Science.gov (United States)

    Enoki, Toshiaki; Kiguchi, Manabu

    2018-03-01

    Interest in utilizing organic molecules to fabricate electronic materials has existed ever since organic (molecular) semiconductors were first discovered in the 1950s. Since then, scientists have devoted serious effort to the creation of various molecule-based electronic systems, such as molecular metals and molecular superconductors. Single-molecule electronics and the associated basic science have emerged over the past two decades and provided hope for the development of highly integrated molecule-based electronic devices in the future (after the Si-based technology era has ended). Here, nanographenes (nano-sized graphene) with atomically precise structures are among the most promising molecules that can be utilized for electronic/spintronic devices. To manipulate single small molecules for an electronic device, a single molecular junction has been developed. It is a powerful tool that allows even small molecules to be utilized. External electric, magnetic, chemical, and mechanical perturbations can change the physical and chemical properties of molecules in a way that is different from bulk materials. Therefore, the various functionalities of molecules, along with changes induced by external perturbations, allows us to create electronic devices that we cannot create using current top-down Si-based technology. Future challenges that involve the incorporation of condensed matter physics, quantum chemistry calculations, organic synthetic chemistry, and electronic device engineering are expected to open a new era in single-molecule device electronic technology.

  1. Double Differential Cross-Sections for Electron Impact Ionization of Atoms and Molecules

    Directory of Open Access Journals (Sweden)

    Mevlut Dogan

    2013-01-01

    Full Text Available The single ionizing collision between an incident electron and an atom/molecule ends up two kinds of outgoing electrons called scattered and ejected electrons. As features of electron impact ionization, these two types of electrons are indistinguishable. Double differential cross-sections (DDCS can be obtained by measuring the energy and angular distributions of one of the two outgoing electrons with an electron analyzer. We used He, Ar, H2, and CH4 targets in order to understand the ionization mechanisms of atomic and molecular systems. We measured differential cross-sections (DCS and double differential cross-sections at 250 eV electron impact energy. The elastic DCSs were measured for He, Ar, H2, and CH4, whereas the inelastic DCSs of He were obtained for 21P excitation level for 200 eV impact electron energy.

  2. All electron ab initio investigations of the electronic states of the FeC molecule

    DEFF Research Database (Denmark)

    Shim, Irene; Gingerich, Karl A.

    1999-01-01

    The low lying electronic states of the molecule FeC have been investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) and multi reference configuration interaction (MRCI) calculations. The relativistic corrections for the one electron Darwin contact term...... state is confirmed as being 3 . The spectroscopic constants for the ground state and eleven excited states have been derived from the results of the MRCI calculations. The spectroscopic constants for the 3 ground state have been determined as re = 1.585 Å and e = 859 cm-1, and for the low-lying 1 state...... as re = 1.567 Å and e = 952 cm-1. The values for the ground state agree well with the available experimental data. The FeC molecule is polar with charge transfer from Fe to C. The dipole moment has been determined as 1.86 D in the 3 ground state and as 1.51 D in the 1 state. From the results of the MRCI...

  3. Physics and chemistry of the influence of excited molecules on combustion enhancement

    Science.gov (United States)

    Starik, A. M.; Loukhovitski, B. I.; Sharipov, A. S.; Titova, N. S

    2015-01-01

    The paper addresses detailed analysis of kinetic processes in the H2−O2, CO−O2 and CH4−O2-reactive systems upon the presence of singlet oxygen molecules O2(a1Δg) and and the influence of the activation of oxygen molecules in electric discharge on the acceleration of ignition in the H2−O2 and CH4−O2 mixtures. The possibility of the intensification of CO oxidation due to excitation of O2 and N2 molecule vibrations and generation of singlet oxygen molecules is also considered. It is shown that the effect of accelerating the ignition strongly depends on the reduced electric field and, as a consequence, on the composition of discharge plasma as well as on the features of chain mechanism development in oxy-fuel systems. It is revealed that the most effective approach for the intensification of CO oxidation both in the moist air and in the products of hydrocarbon combustion in air is the generation of O2(a1Δg) molecules by electric discharge. Computations showed that the presence of 1% O2(a1Δg) in the total oxygen allowed one to convert CO to CO2 even at the temperature T=850–900 K in the time of 10−2 s. The excitation of O2 and N2 molecule vibrations is less effective for such a conversion. PMID:26170425

  4. Infrared-pump-x-ray-probe spectroscopy of vibrationally excited molecules

    Science.gov (United States)

    Ignatova, Nina; da Cruz, Vinícius V.; Couto, Rafael C.; Ertan, Emilie; Odelius, Michael; Ågren, Hans; Guimarães, Freddy F.; Zimin, Andrei; Polyutov, Sergey P.; Gel'mukhanov, Faris; Kimberg, Victor

    2017-04-01

    We develop a theory of infrared (IR)-pump-x-ray-probe spectroscopy for molecular studies. We illustrate advantages of the proposed scheme by means of numerical simulations employing a vibrational wave packet technique applied to x-ray absorption and resonant inelastic x-ray scattering (RIXS) spectra of the water molecule vibrationally excited by a preceding IR field. The promotion of the vibrationally excited molecule to the dissociative 1 a1-14 a1 and bound 1 a1-12 b2 core-excited states with qualitatively different shapes of the potential energy surfaces creates nuclear wave packets localized along and between the OH bonds, respectively. The projection of these wave packets on the final vibrational states, governed by selection and propensity rules, results in spatial selectivity of RIXS sensitive to the initial vibrationally excited state, which makes it possible to probe selectively the ground state properties along different modes. In addition, we propose to use RIXS as a tool to study x-ray absorption from a selected vibrational level of the ground state when the spectral resolution is sufficiently high to resolve vibrational overtones. The proposed technique has potential applications for advanced mapping of multidimensional potential energy surfaces of ground and core-excited molecular states, for symmetry-resolved spectroscopy, and for steering chemical reactions.

  5. Versatile single-molecule multi-color excitation and detection fluorescence setup for studying biomolecular dynamics

    KAUST Repository

    Sobhy, M. A.

    2011-11-07

    Single-molecule fluorescence imaging is at the forefront of tools applied to study biomolecular dynamics both in vitro and in vivo. The ability of the single-molecule fluorescence microscope to conduct simultaneous multi-color excitation and detection is a key experimental feature that is under continuous development. In this paper, we describe in detail the design and the construction of a sophisticated and versatile multi-color excitation and emission fluorescence instrument for studying biomolecular dynamics at the single-molecule level. The setup is novel, economical and compact, where two inverted microscopes share a laser combiner module with six individual laser sources that extend from 400 to 640 nm. Nonetheless, each microscope can independently and in a flexible manner select the combinations, sequences, and intensities of the excitation wavelengths. This high flexibility is achieved by the replacement of conventional mechanical shutters with acousto-optic tunable filter (AOTF). The use of AOTF provides major advancement by controlling the intensities, duration, and selection of up to eight different wavelengths with microsecond alternation time in a transparent and easy manner for the end user. To our knowledge this is the first time AOTF is applied to wide-field total internal reflection fluorescence (TIRF) microscopy even though it has been commonly used in multi-wavelength confocal microscopy. The laser outputs from the combiner module are coupled to the microscopes by two sets of four single-mode optic fibers in order to allow for the optimization of the TIRF angle for each wavelength independently. The emission is split into two or four spectral channels to allow for the simultaneous detection of up to four different fluorophores of wide selection and using many possible excitation and photoactivation schemes. We demonstrate the performance of this new setup by conducting two-color alternating excitation single-molecule fluorescence resonance energy

  6. Photoinduced electron transfer in some photosensitive molecules ...

    Indian Academy of Sciences (India)

    Unknown

    Semiconductor; photocatalytic; photosensitive molecule; intramolecular charge transfer; TiO2/Y-zeolite. 1. Introduction. The consumption of energy has grown exponentially over the last two decades due to rapid industrialization and better living standards throughout the world. Among the various forms of energy available ...

  7. Photoinduced electron transfer in some photosensitive molecules ...

    Indian Academy of Sciences (India)

    Unknown

    Abstract. An intramolecular charge transfer (ICT) molecule, p-N,N-dimethyl- aminobenzoic acid (DMABA) has been studied in zeolite and colloidal media. The ratio of ICT to normal emission (ICT/LE) is greatly enhanced in zeolites compared to that in polar solvents. The ICT emission of DMABA was quenched by increasing ...

  8. Photoinduced electron transfer in some photosensitive molecules ...

    Indian Academy of Sciences (India)

    An intramolecular charge transfer (ICT) molecule, -N,N-dimethylaminobenzoic acid (DMABA) has been studied in zeolite and colloidal media. The ratio of ICT to normal emission (ICT/LE) is greatly enhanced in zeolites compared to that in polar solvents. The ICT emission of DMABA was quenched by increasing the ...

  9. Electron-Molecule Col1isions: Quantitative Approaches, and the Legacy of Aaron Temkin

    Science.gov (United States)

    Schneider, B.I.

    2007-01-01

    This article, on electron-molecule collisions, is dedicated to the legacy of my good friend and sometime collaborator, Aaron Temkin on his retirement from the NASA-Goddard Space Flight Center after many years of work at the highest intellectual level in the theoretical treatment of electron-atom and electron-molecule scattering. Aaron's contributions to the manner in which we think about electron-molecule collisions is clear to all of us who have worked in this field. I doubt that the great progress that has occurred in the computational treatment of such complex collision problems could have happened without these contributions. For a brief historical account, see the discussion of Temkin's contribution to electron-molecule scattering in the first article of this volume by Dr. A. K. Bhatia. In this article, I will concentrate on the application of the so called, non-adiabatic R-matrix theory, to vibrational excitation and dissociative attachment, although I will also present some results applying the Linear Algebraic and Kohn-Variational methods to vibrational excitation. As a starting point for almost all computationally effective approaches to electron-molecule collisions, is the fixed nuclei approximation. That is, one recognizes, just as one does with molecular bound states, that there is a separation of electronic(fast) and nuclear(s1ow) degrees of freedom. This separation makes it possible to "freeze" the nuclei in space, calculate the collision parameters for the frozen molecule and then, somehow to add back the vibrations and rotations. The manner in which this is done, depends on the details of the collision problem. It is the work of Aaron and a number of other researchers that has provided the guidance necessary to resolve these issues.

  10. Excited-state annihilation reduces power dependence of single-molecule FRET experiments.

    Science.gov (United States)

    Nettels, Daniel; Haenni, Dominik; Maillot, Sacha; Gueye, Moussa; Barth, Anders; Hirschfeld, Verena; Hübner, Christian G; Léonard, Jérémie; Schuler, Benjamin

    2015-12-28

    Single-molecule Förster resonance energy transfer (FRET) experiments are an important method for probing biomolecular structure and dynamics. The results from such experiments appear to be surprisingly independent of the excitation power used, in contradiction to the simple photophysical mechanism usually invoked for FRET. Here we show that excited-state annihilation processes are an essential cause of this behavior. Singlet-singlet annihilation (SSA) is a mechanism of fluorescence quenching induced by Förster-type energy transfer between two fluorophores while they are both in their first excited singlet states (S1S1), which is usually neglected in the interpretation of FRET experiments. However, this approximation is only justified in the limit of low excitation rates. We demonstrate that SSA is evident in fluorescence correlation measurements for the commonly used FRET pair Alexa 488/Alexa 594, with a rate comparable to the rate of energy transfer between the donor excited state and the acceptor ground state (S1S0) that is exploited in FRET experiments. Transient absorption spectroscopy shows that SSA occurs exclusively via energy transfer from Alexa 488 to Alexa 594. Excitation-power dependent microsecond correlation experiments support the conclusion based on previously reported absorption spectra of triplet states that singlet-triplet annihilation (STA) analogously mediates energy transfer if the acceptor is in the triplet state. The results indicate that both SSA and STA have a pronounced effect on the overall FRET process and reduce the power dependence of the observed FRET efficiencies. The existence of annihilation processes thus seems to be essential for using FRET as a reliable spectroscopic ruler at the high excitation rates commonly employed in single-molecule spectroscopy.

  11. High power electron beam accelerators for gas laser excitation

    International Nuclear Information System (INIS)

    Kelly, J.G.; Martin, T.H.; Halbleib, J.A.

    1976-06-01

    A preliminary parameter investigation has been used to determine a possible design of a high-power, relativistic electron beam, transversely excited laser. Based on considerations of present and developing pulsed power technology, broad area diode physics and projected laser requirements, an exciter is proposed consisting of a Marx generator, pulse shaping transmission lines, radially converging ring diodes and a laser chamber. The accelerator should be able to deliver approximately 20 kJ of electron energy at 1 MeV to the 10 4 cm 2 cylindrical surface of a laser chamber 1 m long and 0.3 m in diameter in 24 ns with very small azimuthal asymmetry and uniform radial deposition

  12. General theory for environmental effects on (vertical) electronic excitation energies.

    Science.gov (United States)

    Schwabe, Tobias

    2016-10-21

    Almost 70 years ago, the first theoretical model for environmental effects on electronic excitation energies has been derived. Since then, several different interpretations and refined models have been proposed for the perichromic shift of a chromophore due to its surrounding medium. Some of these models are contradictory. Here, the contributing terms are derived within the framework of long-range perturbation theory with the least approximations so far. The derivation is based on a state-specific interpretation of the interaction energies and all terms can be identified with individual properties of either the chromophore or the surroundings, respectively. Further, the much debated contribution due to transition moments coupled to the environment can be verified in the form of a non-resonant excitonic coupling to the dynamic polarizabilities in the environment. These general insights should clarify discussions and interpretations of environmental effects on electronic excitations and should foster the development of new models for the computation of these effects.

  13. Electron-lattice Interaction and Nonlinear Excitations in Cuprate Structures

    International Nuclear Information System (INIS)

    Paulsen, J.; Eschrig, H.; Drechsler, S.L.; Malek, J.

    1995-01-01

    A low temperature lattice modulation of the chains of the YBa 2 Cu 3 O 7 is considered by deriving a Hamiltonian of electron-lattice interaction from density-functional calculations for deformed lattice and solving it for the groundstate. Hubbard-type Coulomb interaction is included. The obtained groundstate is a charge-density-wave state with a pereodicity of four lattice constants and a gap for one-electron excitations of about 1eV, sensitively depending on parameters of the Hamiltonian. There are lots of polaronic and solitonic excitations with formation energies deep in the gap, which can pin the Fermi level and thus produce again metallicity of the chain. They might also contribute to pairing of holes in adjacent CuO 2 -planes. (author)

  14. Electron Spectroscopy: Ultraviolet and X-Ray Excitation.

    Science.gov (United States)

    Baker, A. D.; And Others

    1980-01-01

    Reviews recent growth in electron spectroscopy (54 papers cited). Emphasizes advances in instrumentation and interpretation (52); photoionization, cross-sections and angular distributions (22); studies of atoms and small molecules (35); transition, lanthanide and actinide metal complexes (50); organometallic (12) and inorganic compounds (2);…

  15. Solvent effects on electronic excitations of an organic chromophore

    OpenAIRE

    Zuehlsdorff, Tim Joachim; Haynes, Peter D; Hanke, Felix; Payne, Michael Christopher; Hine, Nicholas DM

    2016-01-01

    In this work we study the solvatochromic shift of a selected low energy excited state of alizarin in water by using a linear-scaling implementation of large-scale time-dependent density functional theory (TDDFT). While alizarin, a small organic dye, is chosen as a simple example of solute-solvent interactions, the findings presented here have wider ramifications for the realistic modelling of dyes, paints and pigment-protein complexes. We find that about 380 molecules of explicit water need t...

  16. Theoretical study of near-threshold electron-molecule scattering

    International Nuclear Information System (INIS)

    Morrison, M.A.

    1989-01-01

    We have been engaged in carrying out a foundation study on problems pertaining to near-threshold nuclear excitations in e-H 2 scattering. The primary goals of this study are: to investigate the severity and nature of the anticipated breakdown of the adiabatic-nuclei (AN) approximation, first for rotation only (in the rigid-rotator approximation), and then for vibration; to determine a data base of accurate ab initio cross sections for this important system; to implement and test accurate, computationally-tractable model potentials for exchange and polarization effects; and to begin the exploration of alternative scattering theories for near-threshold collisions. This study has provided a well-defined theoretical context for our future investigations. Second, it has enabled us to identify and quantify several serious problems in the theory of near-threshold electron-molecule scattering that demand attention. And finally, it has led to the development of some of the theoretical and computational apparatus that will form the foundation of future work. In this report, we shall review our progress to date, emphasizing work completed during the current contract year. 17 refs., 5 figs., 1 tab

  17. Theory of nuclear excitation by electron capture for heavy ions

    Energy Technology Data Exchange (ETDEWEB)

    Gagyi-Palffy, A.

    2006-07-01

    The resonant process of nuclear excitation by electron capture (NEEC) in collisions involving highly-charged ions has been investigated theoretically. NEEC is a rare recombination process in which a free electron is captured into a bound shell of an ion with the simultaneous excitation of the nucleus. Total cross sections for NEEC followed by the radiative decay of the excited nucleus are presented for various collision systems. The possibility to observe the NEEC in scattering experiments with trapped or stored ions was discussed focusing on the cases with the largest calculated resonance strength. As the photons emitted in different channels of the electron recombination process are indistinguishable in the total cross section, the interference between NEEC followed by the radiative decay of the nucleus and radiative recombination was investigated. The angular distribution of the emitted photons in the recombination process provides means to discern the two processes. Angular differential cross sections for the emitted photons in the case of E2 nuclear transitions were presented for several heavy elements. (orig.)

  18. Electron plasma dynamics during autoresonant excitation of the diocotron mode

    Energy Technology Data Exchange (ETDEWEB)

    Baker, C. J., E-mail: cbaker@physics.ucsd.edu; Danielson, J. R., E-mail: jrdanielson@ucsd.edu; Hurst, N. C., E-mail: nhurst@physics.ucsd.edu; Surko, C. M., E-mail: csurko@ucsd.edu [Physics Department, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093 (United States)

    2015-02-15

    Chirped-frequency autoresonant excitation of the diocotron mode is used to move electron plasmas confined in a Penning-Malmberg trap across the magnetic field for advanced plasma and antimatter applications. Plasmas of 10{sup 8} electrons, with radii small compared to that of the confining electrodes, can be moved from the magnetic axis to ≥90% of the electrode radius with near unit efficiency and reliable angular positioning. Translations of ≥70% of the wall radius are possible for a wider range of plasma parameters. Details of this process, including phase and displacement oscillations in the plasma response and plasma expansion, are discussed, as well as possible extensions of the technique.

  19. Pulse train induced rotational excitation and orientation of a polar molecule.

    Science.gov (United States)

    Tyagi, Ashish; Arya, Urvashi; Vidhani, Bhavna; Prasad, Vinod

    2014-08-14

    We investigate theoretically the rotational excitation and field free molecular orientation of polar HBr molecule, interacting with train of ultrashort laser pulses. By adjusting the number of pulses, pulse period and the intensity of the pulse, one can suppress a population while simultaneously enhancing the desired population in particular rotational state. We have used train of laser pulses of different shaped pulse envelopes. The dynamics and orientation of molecules in the presence of pulse train of different shapes is studied and explained. Copyright © 2014 Elsevier B.V. All rights reserved.

  20. Single-Molecule Electronics with Cross- Conjugated Molecules: Quantum Interference, IETS and Non-Equilibrium "Temperatures"

    DEFF Research Database (Denmark)

    Jørgensen, Jacob Lykkebo

    Abstract The idea of using single-molecules as components in electronic devices is fas- cinating. For this idea to come into fruition, a number of technical and theo- retical challenges must be overcome. In this PhD thesis, the electron-phonon interaction is studied for a special class of molecules......, which is characterised by destructive quantum interference. The molecules are cross-conjugated, which means that the two parts of the molecules are conjugated to a third part, but not to each other. This gives rise to an anti-resonance in the trans- mission. In the low bias and low temperature regime......-conjugated molecules. We nd that the vibrational modes that would be expected to dominate, following the propensity, rules are very weak. Instead, other modes are found to be the dominant ones. We study this phenomenon for a number of cross-conjugated molecules, and link these ndings to the anti...

  1. Analytical calculation of spin tunneling effect in single molecule magnet Fe8 with considering quadrupole excitation

    OpenAIRE

    Y Yousefi; H Fakhari; K Muminov; M R Benam

    2018-01-01

    Spin tunneling effect in Single Molecule Magnet Fe8 is studied by instanton calculation technique using SU(3) generalized spin coherent state in real parameter as a trial function. For this SMM, tunnel splitting arises due to the presence of a Berry like phase in action, which causes interference between tunneling trajectories (instantons). For this SMM, it is established that the use of quadrupole excitation (g dependence) changes not only the location of the quenching points, but also the n...

  2. Convergence problems and energetic regions in π excited states of certain conjugated molecules

    International Nuclear Information System (INIS)

    Giambiagi, M.S. de; Giambiagi, M.; Barros, H.G. de P.L. de.

    1980-01-01

    When calculating π bond orders of excited and superexcited states of conjugated molecules, difficulties arise in applying the variation method; besides, the convergence problems involved are well known. For pyridazine, chosen for discussion, 27 states are considered; the convergence problem is envisaged through two criteria in the choice of a parameter introduced in the compromise Hamiltonian. This convergence parameter is related to the variation method. There exist three particular solutions for bond orders, which divide the 27 states into energetical regions. (Author) [pt

  3. State preparation and excited electronic and vibrational behavior in hemes.

    Science.gov (United States)

    Challa, J Reddy; Gunaratne, Tissa C; Simpson, M Cather

    2006-10-12

    The temporally overlapping, ultrafast electronic and vibrational dynamics of a model five-coordinate, high-spin heme in a nominally isotropic solvent environment has been studied for the first time with three complementary ultrafast techniques: transient absorption, time-resolved resonance Raman Stokes, and time-resolved resonance Raman anti-Stokes spectroscopies. Vibrational dynamics associated with an evolving ground-state species dominate the observations. Excitation into the blue side of the Soret band led to very rapid S2 --> S1 decay (sub-100 fs), followed by somewhat slower (800 fs) S1 --> S0 nonradiative decay. The initial vibrationally excited, non-Boltzmann S0 state was modeled as shifted to lower energy by 300 cm(-1) and broadened by 20%. On a approximately 10 ps time scale, the S0 state evolved into its room-temperature, thermal distribution S0 profile largely through VER. Anti-Stokes signals disappear very rapidly, indicating that the vibrational energy redistributes internally in about 1-3 ps from the initial accepting modes associated with S1 --> S0 internal conversion to the rest of the macrocycle. Comparisons of anti-Stokes mode intensities and lifetimes from TRARRS studies in which the initial excited state was prepared by ligand photolysis [Mizutani, T.; Kitagawa, T. Science 1997, 278, 443, and Chem. Rec. 2001, 1, 258] suggest that, while transient absorption studies appear to be relatively insensitive to initial preparation of the electronic excited state, the subsequent vibrational dynamics are not. Direct, time-resolved evaluation of vibrational lifetimes provides insight into fast internal conversion in hemes and the pathways of subsequent vibrational energy flow in the ground state. The overall similarity of the model heme electronic dynamics to those of biological systems may be a sign that the protein's influence upon the dynamics of the heme active site is rather subtle.

  4. Review of electron impact excitation cross sections for copper atom

    Energy Technology Data Exchange (ETDEWEB)

    Winter, N.W.; Hazi, A.U.

    1982-02-01

    Excitation of atomic copper by electron impact plays an important role in the copper vapor laser and accurate cross sections are needed for understanding and modeling laser performance. During the past seven years, there have been several attempts to normalize the relative elastic and inelastic cross sections measured by Trajmar and coworkers. However, each of these efforts have yielded different cross sections, and the uncertainty in the correct normalization of the data has been a source of confusion and concern for the kinetic modeling efforts. This difficulty has motivated us to review previous work on the electron impact excitation of copper atom and to perform new calculations of the inelastic cross sections using the impact parameter method. In this memorandum we review the previous attempts to normalize the experimental data and provide a critical assessment of the accuracy of the resulting cross sections. We also present new theoretical cross sections for the electron impact excitation of the /sup 2/S ..-->.. /sup 2/P/sup 0/ and /sup 2/S ..-->.. /sup 2/D transitions in copper. When the experimental cross sections are renormalized to the results of the impact parameter calculations, they are a factor of three smaller than those published in the latest paper of Trajmar et. al. At impact energies above 60 eV the excitation cross sections obtained with the impact parameter method agree well with the results of the very recent, unpublished, close-coupling calculations of Henry. This agreement suggests that the present normalization of the experimental cross sections is probably the most reliable one obtained to date.

  5. Pulsed laser study of excited states of aromatic molecules absorbed in globular proteins

    International Nuclear Information System (INIS)

    Cooper, M.; Thomas, J.K.

    1977-01-01

    Pyrene and several derivatives of pyrene such as pyrene sulfonic acid, and pyrene butyric acid were incorporated into bovine serum albumin (BSA) in aqueous solution. The pyrene chromophore was subsequently excited by a pulse of uv light (lambda = 3471 A) from a Q switched frequency doubled ruby laser. The lifetime of the pyrene excited singlet and triplet states were monitored by time resolved spectrophotometry. Various molecules, such as O 2 and I - , dissolved in the aqueous phase, diffused into the protein and quenched pyrene excited states. The rates of these reactions were followed under a variety of conditions such as pH and temperature and in the presence of inert additives. The rates of pyrene excited-state quenching were often considerably smaller than the rates observed in simple solutions. A comparison of the rates in the protein and homogeneous solutions gives information on the factors such as temperature, charge, and pH that control the movement of small molecules in and into BSA

  6. Attosecond dynamics of electron correlation in doubly excited atomic states

    Energy Technology Data Exchange (ETDEWEB)

    Nicolaides, Cleanthes A. [Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens (Greece) and Physics Department, National Technical University, Athens (Greece)). E-mail: can@eie.gr] Mercouris, Theodoros; Komninos, Yanis [Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens (Greece)]. E-mails: thmerc@eie.gr; ykomn@eie.gr

    2002-06-28

    We have solved the time-dependent Schroedinger equation describing the simultaneous interaction of the He 1s2s {sup 1}S state with two laser-generated pulses of trapezoidal or Gaussian shape, of duration 86 fs and of frequencies {omega}{sub 1}=1.453 au and {omega}{sub 2}=1.781 au. The system is excited to the energy region of two strongly correlated doubly excited states, chosen for this study according to specific criteria. It is demonstrated quantitatively that, provided one focuses on the dynamics occurring within the attosecond timescale, the corresponding orbital configurations, 2s2p and 2p3d {sup 1}P{sup 0}, exist as nonstationary states, with occupation probabilities that are oscillating as the states decay exponentially into the 1s{epsilon}p continuum, during and after the laser-atom interaction. It follows that it is feasible to probe by attosecond pulses the motion of configurations of electrons as they correlate via the total Hamiltonian. For the particular system studied here, the probe pulses could register the oscillating doubly excited configurations by de-exciting to the He 1s3d {sup 1}D state, which emits at 6680 A. (author). Letter-to-the-editor.

  7. Electronic structure of Fe- vs. Ru-based dye molecules

    DEFF Research Database (Denmark)

    Johnson, Phillip S.; Cook, Peter L.; Zegkinoglou, Ioannis

    2013-01-01

    In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold, octah...

  8. Benchmarks for electronically excited states: Time-dependent density functional theory and density functional theory based multireference configuration interaction

    DEFF Research Database (Denmark)

    Silva-Junior, Mario R.; Schreiber, Marko; Sauer, Stephan P. A.

    2008-01-01

    Time-dependent density functional theory (TD-DFT) and DFT-based multireference configuration interaction (DFT/MRCI) calculations are reported for a recently proposed benchmark set of 28 medium-sized organic molecules. Vertical excitation energies, oscillator strengths, and excited-state dipole...... moments are computed using the same geometries (MP2/6-31G*) and basis set (TZVP) as in our previous ab initio benchmark study on electronically excited states. The results from TD-DFT (with the functionals BP86, B3LYP, and BHLYP) and from DFT/MRCI are compared against the previous high-level ab initio...

  9. Elastic scattering of low energy electrons by hydrogen molecule

    International Nuclear Information System (INIS)

    Freitas, L.C.G.; Mu-Tao, L.; Botelho, L.F.

    1987-01-01

    The coherent version of the Renormalized Multiple-Centre Potential Model (RMPM) has been extended to treat the elastic scattering of low energy electrons by H2 molecule. The intramolecular Multiple Scattering (MS) effect has also been included. The comparison against the experimental data shows that the inclusion of the MS improves significantly with experiment. The extension of the present method to study electron-polyatomic molecule interaction is also discussed. (author) [pt

  10. Excited states 2

    CERN Document Server

    Lim, Edward C

    2013-01-01

    Excited States, Volume 2 is a collection of papers that deals with molecules in the excited states. The book describes the geometries of molecules in the excited electronic states. One paper describes the geometries of a diatomic molecule and of polyatomic molecules; it also discusses the determination of the many excited state geometries of molecules with two, three, or four atoms by techniques similar to diatomic spectroscopy. Another paper introduces an ordered theory related to excitons in pure and mixed molecular crystals. This paper also presents some experimental data such as those invo

  11. Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

    International Nuclear Information System (INIS)

    Chu, P.M.Y.

    1991-10-01

    The vibrational to translational (V→T) energy transfer in collisions between large highly vibrationally excited polyatomics and rare gases was investigated by time-of-flight techniques. Two different methods, UV excitation followed by intemal conversion and infrared multiphoton excitation (IRMPE), were used to form vibrationally excited molecular beams of hexafluorobenzene and sulfur hexafluoride, respectively. The product translational energy was found to be independent of the vibrational excitation. These results indicate that the probability distribution function for V→T energy transfer is peaked at zero. The collisional relaxation of large polyatomic molecules with rare gases most likely occurs through a rotationally mediated process. Photodissociation of nitrobenzene in a molecular beam was studied at 266 nm. Two primary dissociation channels were identified including simple bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy radical. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Secondary dissociation of the phenoxy radicals to carbon monoxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne. A supersonic methyl radical beam source is developed. The beam source configuration and conditions were optimized for CH 3 production from the thermal decomposition of azomethane. Elastic scattering of methyl radical and neon was used to differentiate between the methyl radicals and the residual azomethane in the molecular beam

  12. Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

    Energy Technology Data Exchange (ETDEWEB)

    Chu, P.M.Y.

    1991-10-01

    The vibrational to translational (V{yields}T) energy transfer in collisions between large highly vibrationally excited polyatomics and rare gases was investigated by time-of-flight techniques. Two different methods, UV excitation followed by intemal conversion and infrared multiphoton excitation (IRMPE), were used to form vibrationally excited molecular beams of hexafluorobenzene and sulfur hexafluoride, respectively. The product translational energy was found to be independent of the vibrational excitation. These results indicate that the probability distribution function for V{yields}T energy transfer is peaked at zero. The collisional relaxation of large polyatomic molecules with rare gases most likely occurs through a rotationally mediated process. Photodissociation of nitrobenzene in a molecular beam was studied at 266 nm. Two primary dissociation channels were identified including simple bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy radical. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Secondary dissociation of the phenoxy radicals to carbon monoxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne. A supersonic methyl radical beam source is developed. The beam source configuration and conditions were optimized for CH{sub 3} production from the thermal decomposition of azomethane. Elastic scattering of methyl radical and neon was used to differentiate between the methyl radicals and the residual azomethane in the molecular beam.

  13. Collision dynamics of methyl radicals and highly vibrationally excited molecules using crossed molecular beams

    Energy Technology Data Exchange (ETDEWEB)

    Chu, Pamela Mei-Ying [Univ. of California, Berkeley, CA (United States)

    1991-10-01

    The vibrational to translational (V→T) energy transfer in collisions between large highly vibrationally excited polyatomics and rare gases was investigated by time-of-flight techniques. Two different methods, UV excitation followed by intemal conversion and infrared multiphoton excitation (IRMPE), were used to form vibrationally excited molecular beams of hexafluorobenzene and sulfur hexafluoride, respectively. The product translational energy was found to be independent of the vibrational excitation. These results indicate that the probability distribution function for V→T energy transfer is peaked at zero. The collisional relaxation of large polyatomic molecules with rare gases most likely occurs through a rotationally mediated process. Photodissociation of nitrobenzene in a molecular beam was studied at 266 nm. Two primary dissociation channels were identified including simple bond rupture to produce nitrogen dioxide and phenyl radical and isomerization to form nitric oxide and phenoxy radical. The time-of-flight spectra indicate that simple bond rupture and isomerization occurs via two different mechanisms. Secondary dissociation of the phenoxy radicals to carbon monoxide and cyclopentadienyl radicals was observed as well as secondary photodissociation of phenyl radical to give H atom and benzyne. A supersonic methyl radical beam source is developed. The beam source configuration and conditions were optimized for CH3 production from the thermal decomposition of azomethane. Elastic scattering of methyl radical and neon was used to differentiate between the methyl radicals and the residual azomethane in the molecular beam.

  14. Trapped electronic states in YAG crystal excited by femtosecond radiation

    Energy Technology Data Exchange (ETDEWEB)

    Zavedeev, E.V.; Kononenko, V.V.; Konov, V.I. [General Physics Institute of RAS, Moscow (Russian Federation); National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow (Russian Federation)

    2017-07-15

    The excitation of an electronic subsystem of an yttrium aluminum garnet by 800 nm femtosecond radiation was studied theoretically and experimentally. The spatio-temporal dynamics of the refractive index (n) inside the beam waist was explored by means of the pump-probe interferometric technique with a submicron resolution. The observed increase in n indicated the formation of bound electronic states relaxed for ∝ 150 ps. We showed that the experimental data agreed with the computational simulation based on the numerical solution of the nonlinear Schroedinger equation only if these transient states were considered to arise from a direct light-induced process but not from the decay of radiatively generated free-electron-hole pairs. (orig.)

  15. Selectivity in Threshold Vibrational Excitation of CO2 by Electron Impact

    Science.gov (United States)

    Vanroose, W.; Zhang, Zhijong; McCurdy, C. W.; Rescigno, T. N.

    2003-10-01

    Vibrational excitation of the hydrogen halides by low energy electron impact has been a subject of continued interest ever since pronounced threshold peaks were observed in the vibrationally inelastic cross sections by Rohr and Linder some twenty-five years ago. More recently, similar structures were observed in non-polar triatomic molecules, but only for certain transitions. We present a non-empirical local potential model for studying threshold vibrational excitation by electron impact. This work builds on the zero-range potential virtual state model of Gauyacq and Herzenberg (J. P. Gauyacq and A. Herzenberg, Phys. Rev. A 25, 2959 (1982)), using known analytic properties of the S-matrix to predict the analytic continuation of the negative ion potential curve into the continuum. We derive an equation that determines the nuclear dynamics which can be solved without the need for an expansion in target vibrational states. The model is applied to CO2 vibrational excitation and provides, for the first time, a quantitatively accurate description of the observed excitation cross sections at energies below 1 eV.

  16. An exactly solvable model for multiphoton excitation of polyatomic molecules in the presence of collisions

    International Nuclear Information System (INIS)

    Strekalov, M L

    2013-01-01

    A theoretical study has been made on the non-stationary phenomena in the relaxation of highly vibrationally excited molecules under laser radiation giving rise to these molecules. An exact analytical solution to the master equation has been obtained in terms of Meixner polynomials with regard to VV and VT processes. The time-dependent vibrational distribution is used to obtain analytical expressions for the mean number of photons, stored on the vibrational degrees of freedom and transferred to a thermal bath. Using the latter result, an explicit expression is given for the average energy transfer as a function of time. Its dependence on the partial pressure of absorbing molecules has also been established. (paper)

  17. Dissociative electron attachment and electronic excitation in Fe(CO)5

    Czech Academy of Sciences Publication Activity Database

    Allan, M.; Lacko, M.; Papp, P.; Matejčík, Š.; Zlatar, M.; Fabrikant, I. I.; Kočišek, Jaroslav; Fedor, Juraj

    2018-01-01

    Roč. 20, č. 17 (2018), s. 11692-11701 ISSN 1463-9076 R&D Projects: GA ČR GA17-04844S Grant - others:COST(XE) CM1301 Institutional support: RVO:61388955 Keywords : electrons * FEBID * electronic excitation Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 4.123, year: 2016

  18. Electronic excited states and relaxation dynamics in polymer heterojunction systems

    Science.gov (United States)

    Ramon, John Glenn Santos

    , we examine the effect of the nanoscale interfacial morphology and solvation on the electronic excited states of TFB/F8BT. Here, we employ time-dependent density functional theory (TD-DFT) to investigate the relevant excited states of two stacking configurations. We show that the calculated states agree with the excited states responsible for the experimentally observed emission peaks and that these states are blue shifted relative to those of the isolated chain. Furthermore, slight lateral shifts in the stacking orientation not only shift the excited state energies; more importantly, they alter the nature of these states altogether. Lastly, we see that solvation greatly stabilizes the charge-transfer states.

  19. Computer simulation of electronic excitation in atomic collision cascades

    Energy Technology Data Exchange (ETDEWEB)

    Duvenbeck, A.

    2007-04-05

    The impact of an keV atomic particle onto a solid surface initiates a complex sequence of collisions among target atoms in a near-surface region. The temporal and spatial evolution of this atomic collision cascade leads to the emission of particles from the surface - a process usually called sputtering. In modern surface analysis the so called SIMS technology uses the flux of sputtered particles as a source of information on the microscopical stoichiometric structure in the proximity of the bombarded surface spots. By laterally varying the bombarding spot on the surface, the entire target can be scanned and chemically analyzed. However, the particle detection, which bases upon deflection in electric fields, is limited to those species that leave the surface in an ionized state. Due to the fact that the ionized fraction of the total flux of sputtered atoms often only amounts to a few percent or even less, the detection is often hampered by rather low signals. Moreover, it is well known, that the ionization probability of emitted particles does not only depend on the elementary species, but also on the local environment from which a particle leaves the surface. Therefore, the measured signals for different sputtered species do not necessarily represent the stoichiometric composition of the sample. In the literature, this phenomenon is known as the Matrix Effect in SIMS. In order to circumvent this principal shortcoming of SIMS, the present thesis develops an alternative computer simulation concept, which treats the electronic energy losses of all moving atoms as excitation sources feeding energy into the electronic sub-system of the solid. The particle kinetics determining the excitation sources are delivered by classical molecular dynamics. The excitation energy calculations are combined with a diffusive transport model to describe the spread of excitation energy from the initial point of generation. Calculation results yield a space- and time-resolved excitation

  20. Momentum-space calculation of electron-molecule scattering

    International Nuclear Information System (INIS)

    McCarthy, I.E.; Rossi, A.M.

    1994-01-01

    The momentum-space calculation of electron-molecule elastic scattering is described and illustrated as the first step in a program of electron-molecule scattering that takes all reaction channels into account. The method is the analog for molecules of the integral-equation methods that have had essentially complete success for structurally simple atoms. Although scattering is a single-center problem in momentum space its multicentered nature in coordinate space results in the integral equations for different orbital angular momenta being coupled. There are no restrictions in principle on the nature of the target molecule. For illustrative purposes the static exchange calculation is supplemented by a phenomenological polarization potential that will be replaced by an ab initio optical potential and coupled electronic channels in the planned development of a general scattering method

  1. Compilation of electron collision excitation cross sections for neutro argon

    International Nuclear Information System (INIS)

    Blanco Ramos, F.

    1993-01-01

    The present work presents a compilation and critical analysis of the available data on electron collision excitation cross sections for neutral Argon levels. This study includes: 1.- A detailed description in intermediate coupling for all the levels belonging the 20 configurations 3p''5 ns(n=4 to 12), np(n=4 to 8) and nd(n=3 to 8) of neutral Argon. 2.- Calculation of the electron collision excitation cross sections in Born and Born-Oppenheimer-Ochkur approximations for all the levels in the 14 configurations 3p''5 ns(n=4 to 7), np(n=4 to 7) and nd(n=3 to 8). 3.- Comparison and discussion of the compiled data. These are the experimental and theoretical values available from the literature, and those from this work. 4.- Analysis of the regularities and systematic behaviors in order to determine which values can be considered more reliable. It is show that the concept of one electron cross section results quite useful for this purpose. In some cases it has been possible to obtain in this way approximate analytical expressions interpolating the experimental data. 5.- All the experimental and theoretical values studied are graphically presented and compared. 6.- The last part of the work includes a listing of several general purpose programs for Atomic Physics calculations developed for this work. (Author)

  2. Compilation of electron collision excitation cross sections for neutral argon

    International Nuclear Information System (INIS)

    Blanco, F.

    1993-01-01

    The present work presents a compilation and critical analysis of the available data on electron collision excitation cross sections for neutral Argon levels. This study includes: 1.- A detailed description in intermediate coupling for all the levels belonging the 20 configurations 3p5 ns (n=4to 12), np(n=4to8) and nd(n=3to8)of neutral Argon. 2.- Calculation of the electron collision excitation cross sections in Born and Born-Oppenheimer-Ochkur approximations for all the levels in the 14 configurations 3p5 ns (n=4 to 7), np (n=4 to 7) and nd (n=3 to 8). 3.- comparison and discussion of the compiled data. These are the experimental and theoretical values available from the literature, and those from this work. 4.- Analysis of the regularities and systematic behaviors in order to determine which values can be considered more reliable. It is show that the concept of one electron cross section results quite useful for this purpose. In some cases it has been possible to obtain in this way approximate analytical expressions interpolating the experimental data. 5.- All the experimental and theoretical values studied are graphically presented and compared. 6.- The last part of the work includes a listing of several general purpose programs for Atomic Physics calculations developed for this work. (Author) 35 refs

  3. Theoretical study of near-threshold electron-molecule scattering. Progress report

    International Nuclear Information System (INIS)

    Morrison, M.A.

    1984-07-01

    Theoretical calculation of accurate low-energy electron-molecule cross sections requires: (1) an accurate interaction potential; and (2) a computationally-tractable formulation of the collision theory. The potential must be free of parameters that require adjustment to experimental cross sections. Moreover, near the threshold for a nuclear excitation the collision theory must accurately - if approximately - take account of the coupling of the nuclear dynamics and the (quantal) motion of the scattering electron. Progress has been made on two facets of the electron-molecule interaction: exchange and polarization effects. Our tuned free-electron-gas exchange potential has been generalized to allow for vibrational excitation, and, more interestingly, the validity of this model for nuclear excitations has been studied. A procedure for determining an ab initio (parameter-free) polarization potential that takes (approximate) account of non-adiabatic effects has been implemented and tested for e-H 2 scattering. Results calculated with this model potential agree well with those of benchmark optical-potential studies

  4. Classification of Feshbach resonances in electron-molecule scattering

    International Nuclear Information System (INIS)

    Spence, D.

    1976-01-01

    Certain systematics are derived which often enable a simple determination of resonance configurations in electron-molecule scattering by making a comparison between resonance spectra and known Rydberg-state spectra. The determination of resonance grandparent states and the systematics of the binding energies of pairs of Rydberg electrons in diatomic molecules, the systematics of the binding energies of electrons with various values of n and l to parent Rydberg states, and an application of guidelines provided by the above systematics to new systems are treated. 19 refs

  5. 48-spot single-molecule FRET setup with periodic acceptor excitation

    Science.gov (United States)

    Ingargiola, Antonino; Segal, Maya; Gulinatti, Angelo; Rech, Ivan; Labanca, Ivan; Maccagnani, Piera; Ghioni, Massimo; Weiss, Shimon; Michalet, Xavier

    2018-03-01

    Single-molecule Förster resonance energy transfer (smFRET) allows measuring distances between donor and acceptor fluorophores on the 3-10 nm range. Solution-based smFRET allows measurement of binding-unbinding events or conformational changes of dye-labeled biomolecules without ensemble averaging and free from surface perturbations. When employing dual (or multi) laser excitation, smFRET allows resolving the number of fluorescent labels on each molecule, greatly enhancing the ability to study heterogeneous samples. A major drawback to solution-based smFRET is the low throughput, which renders repetitive measurements expensive and hinders the ability to study kinetic phenomena in real-time. Here we demonstrate a high-throughput smFRET system that multiplexes acquisition by using 48 excitation spots and two 48-pixel single-photon avalanche diode array detectors. The system employs two excitation lasers allowing separation of species with one or two active fluorophores. The performance of the system is demonstrated on a set of doubly labeled double-stranded DNA oligonucleotides with different distances between donor and acceptor dyes along the DNA duplex. We show that the acquisition time for accurate subpopulation identification is reduced from several minutes to seconds, opening the way to high-throughput screening applications and real-time kinetics studies of enzymatic reactions such as DNA transcription by bacterial RNA polymerase.

  6. Low-energy electron-impact excitation of the 3,1A2(n→π*) states of formaldehyde

    International Nuclear Information System (INIS)

    Sun, Q.; Winstead, C.; McKoy, V.; Germano, J.S.E.; Lima, M.A.P.

    1992-01-01

    A three-state calculation of electron-impact excitation of formaldehyde to the a 3 A 2 and A 1 A 2 states is carried out using the Schwinger multichannel variational method. The integral and differential cross sections so obtained agree fairly well with theoretical results obtained using the complex Kohn method. Though agreement between the calculated integral cross section and the single available experimental measurement is qualitative, similar conclusions regarding the excitation mechanism are reached. A generalization of the selection rule for (Σ + ↔Σ - ) electron-impact excitation of diatomic molecules is used to explain the shape of the differential cross sections for the a 3 A 2 and A 1 A 2 excitations

  7. Stability of sulfate complexes of electronically excited uranyl

    Energy Technology Data Exchange (ETDEWEB)

    Ostakhov, S.S.; Kazakov, V.P.; Afonichev, D.D. [Inst. of Organic Chemistry, Ufa (Russian Federation)

    1995-11-01

    The complex formation of electronically excited uranyl ions with SO{sub 4}{sup 2-}anions in 0.1 M aqueous HClO{sub 4} has been studied by time-resolved luminescence spectroscopy. The stability constants of uranyl sulfate complexes (UO{sub 2}SO{sub 4}) (K=870 1 mol{sup -1}) and [UO{sub 2}(SO{sub 4}){sub 2}{sup 2-}](K=47000 1 mol{sup -1}) in excited state have been determined; they are more than an order of magnitude greater than those reported for complex formation of uranyl ions in the ground state. The complex formation of uranyl with sulfate ions is accompanied by the increase of the quantum yield of the uranyl lumenescence. The maxima of luminescence and absorption bands of uranyl ions are shifted with increasing the total concentration of SO{sub 4}{sup 2-} in solution, which supports the data obtained. The shift of the maxima of luminescence bands is observed at a sulfate concentration that is considerably lower than that causing the same shift of the maxima of the absorption bands. Such effect is consistent with the calculated stability constants of sulfate complexes of excited uranyl ions.

  8. Analysis of Atomic Electronic Excitation in Nonequilibrium Air Plasmas

    International Nuclear Information System (INIS)

    He Xin; Jia Hong-Hui; Yin Hong-Wei; Zhang Hai-Liang; Chang Sheng-Li; Yang Jun-Cai; Dang Wei-Hua

    2014-01-01

    Electronic excitation of atoms is studied in nonequilibrium air plasmas with the electronic temperature between 8000 K and 20000 K. By using the modified Saha—Boltzmann equation, our simplified method takes into account significant radiative processes and strong self-absorption of the vacuum ultraviolet lines. Calculations are carried out at three trajectory points of the Fire II flight experiment. Good agreement with the detailed collisional-radiative model is obtained, and the performance of this method in applications to highly nonequilibrium conditions is better than Park's quasi-steady-state model and Spradian-9.0. A short discussion on the influence of optical thickness of the vacuum ultraviolet radiation is also given. It costs about 2.9 ms on the average to solve one cell of the shock layer on a low cost computer, which shows that the present method is fast and efficient. (physics of gases, plasmas, and electric discharges)

  9. Analytical calculation of spin tunneling effect in single molecule magnet Fe8 with considering quadrupole excitation

    Directory of Open Access Journals (Sweden)

    Y Yousefi

    2018-02-01

    Full Text Available Spin tunneling effect in Single Molecule Magnet Fe8 is studied by instanton calculation technique using SU(3 generalized spin coherent state in real parameter as a trial function. For this SMM, tunnel splitting arises due to the presence of a Berry like phase in action, which causes interference between tunneling trajectories (instantons. For this SMM, it is established that the use of quadrupole excitation (g dependence changes not only the location of the quenching points, but also the number of these points. Also, these quenching points are the steps in hysteresis loops of this SMM. If dipole and quadrupole excitations in classical energy considered, the number of these steps equals to the number that obtained from experimental data.

  10. Coherence, energy and charge transfers in de-excitation pathways of electronic excited state of biomolecules in photosynthesis

    DEFF Research Database (Denmark)

    Bohr, Henrik; Malik, F. Bary

    2013-01-01

    The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin–chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used F¨orster–Dexter th...

  11. ESR measurement of the concentration of vibrationally excited hydrogen and deuterium molecules

    International Nuclear Information System (INIS)

    Gershenzon, Yu.M.; Ivanov, A.V.; Il'in, S.D.; Kucheryavyi, S.I.; Rozenshtein, V.B.

    1988-01-01

    A method is described for measuring the concentration of vibrationally excited H 2 and D 2 molecules using an ESR microwave spectrometer. The essence of the method is the titration of H 2 (v = 1) and D 2 (v = 1) with D and H atoms and measurement of the concentrations of the titration products H and D, respectively. Stoichiometric titration coefficients were determined in the form of proportionality coefficients between the titration signals Δ[H], Δ[D] and the concentrations of H 2 (v = 1), D 2 (v = 1)

  12. Analytic energy gradient of excited electronic state within TDDFT/MMpol framework: Benchmark tests and parallel implementation.

    Science.gov (United States)

    Zeng, Qiao; Liang, WanZhen

    2015-10-07

    The time-dependent density functional theory (TDDFT) has become the most popular method to calculate the electronic excitation energies, describe the excited-state properties, and perform the excited-state geometric optimization of medium and large-size molecules due to the implementation of analytic excited-state energy gradient and Hessian in many electronic structure software packages. To describe the molecules in condensed phase, one usually adopts the computationally efficient hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) models. Here, we extend our previous work on the energy gradient of TDDFT/MM excited state to account for the mutual polarization effects between QM and MM regions, which is believed to hold a crucial position in the potential energy surface of molecular systems when the photoexcitation-induced charge rearrangement in the QM region is drastic. The implementation of a simple polarizable TDDFT/MM (TDDFT/MMpol) model in Q-Chem/CHARMM interface with both the linear response and the state-specific features has been realized. Several benchmark tests and preliminary applications are exhibited to confirm our implementation and assess the effects of different treatment of environmental polarization on the excited-state properties, and the efficiency of parallel implementation is demonstrated as well.

  13. Low energy electron attachment to the uracil molecule

    International Nuclear Information System (INIS)

    Hanel, G.; Gstir, B.; Denifl, S.; Scheier, P.; Maerk, T.D.; Farizon, B.; Farizon, M.

    2002-01-01

    Using a recently constructed high resolution crossed beam apparatus involving a hemispherical electron monochromator, electron attachment to the uracil molecule C 4 H 4 N 2 O 2 was studied. The electron energy range investigated was in the region between 0 and 12 eV. What will happen when slow electrons are colliding with the cellular RNA compound uracil was the objective of this investigation. The following anion fragments were detected: (C 4 H 3 N 2 O 2 ) - , OCN - , (H 2 C 3 NO) - , CN - , O - . The most important result was that within the detection efficiency any traces of the parent anion were observed. The most intense fragment anion appeared on a mass to charge ratio 111 amu., it corresponds to a uracil molecule missing one hydrogen. Another observation was whereas the parent minus H anion is observed at zero electron energy, all other fragments appear in other range. (nevyjel)

  14. Single-Molecule Electronics: Chemical and Analytical Perspectives.

    Science.gov (United States)

    Nichols, Richard J; Higgins, Simon J

    2015-01-01

    It is now possible to measure the electrical properties of single molecules using a variety of techniques including scanning probe microcopies and mechanically controlled break junctions. Such measurements can be made across a wide range of environments including ambient conditions, organic liquids, ionic liquids, aqueous solutions, electrolytes, and ultra high vacuum. This has given new insights into charge transport across molecule electrical junctions, and these experimental methods have been complemented with increasingly sophisticated theory. This article reviews progress in single-molecule electronics from a chemical perspective and discusses topics such as the molecule-surface coupling in electrical junctions, chemical control, and supramolecular interactions in junctions and gating charge transport. The article concludes with an outlook regarding chemical analysis based on single-molecule conductance.

  15. Effective collision strengths for electron impact excitation of Cl III

    CERN Document Server

    Ramsbottom, C A; Keenan, F P

    2001-01-01

    Effective collision strengths for electron-impact excitation of the phosphorus-like ion Cl III are presented for all fine-structure transitions among the levels arising from the lowest 23 LS states. The collisional cross sections are computed in the multichannel close-coupling R-matrix approximation, where sophisticated configuration-interaction wave functions are used to represent the target states. The 23 LS states are formed from the basis configurations 3s sup 2 3p sup 3 , 3s3p sup 4 , 3s sup 2 3p sup 2 3d, and 3s sup 2 3p sup 2 4s, and correspond to 49 fine-structure levels, leading to a total possible 1176 fine-structure transitions. The effective collision strengths, obtained by averaging the electron collision strengths over a Maxwellian distribution of electron velocities, are tabulated in this paper for all 1176 transitions and for electron temperatures in the ranges T(K)=7500-25,000 and log T(K)=4.4-5.4. The former range encompasses the temperatures of particular importance for application to gaseo...

  16. Calculation of the ground and excited states of the Ne2 molecule by the variational cellular method

    International Nuclear Information System (INIS)

    Dias, A.M.; Rosato, A.

    1981-07-01

    The potential curves for the ground state 1 Σ + sub(g) and for the first singlet excited state 1 Σ + sub (u) of the Ne 2 molecule are determined by the Variational Cellular Method. From these curves some spectroscopical constants are obtained. Ionization energies of the excited state 1 Σ + sub (u) are calculated. (Author) [pt

  17. Calculation of the ground and excited states of the Ne2 molecule by the Variational Cellular Method

    International Nuclear Information System (INIS)

    Dias, A.M.; Rosato, A.

    1982-01-01

    The potential curves for the ground 1 μ + sub(g) and for the first singlet excited state 1 μ + sub(u) of the Ne 2 molecule are determined by the Variational Cellular Method. From these curves some spectroscopical constants are obtained. Ionization energies of the excited state 1 μ + sub(u) are calculated. (Author) [pt

  18. Absence of quantum oscillations in electronic excitation transfer in the Fenna-Matthews-Olson complex

    Science.gov (United States)

    Eisfeld, Alexander; Ritschel, Gerhard; Roden, Jan; Strunz, Walter; Aspuru-Guzik, Alan

    2012-02-01

    Energy transfer in the photosynthetic Fenna-Matthews-Olson (FMO) complex of the Green Sulfur Bacteria is studied theoretically taking all three subunits (monomers) of the FMO trimer and the recently found eighth bacteriochlorophyll (BChl) molecule into account. For the calculations we use the efficient Non-Markovian Quantum State diffusion approach. Since it is believed that the eighth BChl is located near the main light harvesting antenna we look at the differences in transfer between the situation when BChl 8 is initially excited and the usually considered case when BChl 1 or 6 is initially excited. We find strong differences in the transfer dynamics, both qualitatively and quantitatively. When the excited state dynamics is initialized at site eight of the FMO complex, we see a slow exponential-like decay of the excitation. This is in contrast to the oscillations and a relatively fast transfer that occurs when only seven sites or initialization at sites 1 and 6 is considered. Additionally we show that differences in the values of the electronic transition energies found in the literature lead to a large difference in the transfer dynamics.

  19. Lessons on electronic decoherence in molecules from exact modeling

    Science.gov (United States)

    Hu, Wenxiang; Gu, Bing; Franco, Ignacio

    2018-04-01

    Electronic decoherence processes in molecules and materials are usually thought and modeled via schemes for the system-bath evolution in which the bath is treated either implicitly or approximately. Here we present computations of the electronic decoherence dynamics of a model many-body molecular system described by the Su-Schrieffer-Heeger Hamiltonian with Hubbard electron-electron interactions using an exact method in which both electronic and nuclear degrees of freedom are taken into account explicitly and fully quantum mechanically. To represent the electron-nuclear Hamiltonian in matrix form and propagate the dynamics, the computations employ the Jordan-Wigner transformation for the fermionic creation/annihilation operators and the discrete variable representation for the nuclear operators. The simulations offer a standard for electronic decoherence that can be used to test approximations. They also provide a useful platform to answer fundamental questions about electronic decoherence that cannot be addressed through approximate or implicit schemes. Specifically, through simulations, we isolate basic mechanisms for electronic coherence loss and demonstrate that electronic decoherence is possible even for one-dimensional nuclear bath. Furthermore, we show that (i) decreasing the mass of the bath generally leads to faster electronic decoherence; (ii) electron-electron interactions strongly affect the electronic decoherence when the electron-nuclear dynamics is not pure-dephasing; (iii) classical bath models with initial conditions sampled from the Wigner distribution accurately capture the short-time electronic decoherence dynamics; (iv) model separable initial superpositions often used to understand decoherence after photoexcitation are only relevant in experiments that employ delta-like laser pulses to initiate the dynamics. These insights can be employed to interpret and properly model coherence phenomena in molecules.

  20. Excitation of the 4.3-μm bands of CO2 by low-energy electrons

    International Nuclear Information System (INIS)

    Bulos, R.R.; Phelps, A.V.

    1976-01-01

    Rate coefficients for the excitation of the 4.3-μm bands of CO 2 by low-energy electrons in CO 2 have been measured using a drift-tube technique. The CO 2 density [(1.5 to 7) x 10 17 molecules/cm 3 ] was chosen to maximize the radiation reaching the detector. Line-by-line transmission calculations were used to take into account the absorption of 4.3-μm radiation. A small fraction of the approximately 10 -8 W of the 4.3-μm radiation produced by the approximately 10 -7 -A electron current was incident on an InSb photovoltaic detector. The detector calibration and absorption calculations were checked by measuring the readily calculated excitation coefficients for vibrational excitation of N 2 containing a small concentration of CO 2 . For pure CO 2 the number of molecules capable of emitting 4.3-μm radiation produced per cm of electron drift and per CO 2 molecule varied from 10 -17 cm -2 at E/N = 6 x 10 -17 V cm 2 to 5.4 x 10 -16 cm -2 at E/N = 4 x 10 -16 V cm 2 . Here E is the electric field and N is total gas density. The excitation coefficients at lower E/N are much larger than estimated previously. A set of vibrational excitation cross sections is obtained for CO 2 which is consistent with the excitation coefficient data and with most of the published electron-beam data

  1. Sign Changes in the Electric Dipole Moment of Excited States in Rubidium-Alkaline Earth Diatomic Molecules

    Science.gov (United States)

    Pototschnig, Johann V.; Lackner, Florian; Hauser, Andreas W.; Ernst, Wolfgang E.

    2015-06-01

    In a recent series of combined experimental and theoretical studies we investigated the ground state and several excited states of the Rb-alkaline earth molecules RbSr and RbCa. The group of alkali-alkaline earth (AK-AKE) molecules has drawn attention for applications in ultracold molecular physics and the measurement of fundamental constants due to their large permanent electric and magnetic dipole moments in the ground state. These properties should allow for an easy manipulation of the molecules and simulations of spin models in optical lattices. In our studies we found that the permanent electric dipole moment points in different directions for certain electronically excited states, and changes the sign in some cases as a function of bond length. We summarize our results, give possible causes for the measured trends in terms of molecular orbital theory and extrapolate the tendencies to other combinations of AK and AKE - elements. F. Lackner, G. Krois, T. Buchsteiner, J. V. Pototschnig, and W. E. Ernst, Phys. Rev. Lett., 2014, 113, 153001; G. Krois, F. Lackner, J. V. Pototschnig, T. Buchsteiner, and W. E. Ernst, Phys. Chem. Chem. Phys., 2014, 16, 22373; J. V. Pototschnig, G. Krois, F. Lackner, and W. E. Ernst, J. Chem. Phys., 2014, 141, 234309 J. V. Pototschnig, G. Krois, F. Lackner, and W. E. Ernst, J. Mol. Spectrosc., in Press (2015), doi:10.1016/j.jms.2015.01.006 M. Kajita, G. Gopakumar, M. Abe, and M. Hada, J. Mol. Spectrosc., 2014, 300, 99-107 A. Micheli, G. K. Brennen, and P. Zoller, Nature Physics, 2006, 2, 341-347

  2. Transition and Electron Impact Excitation Collision Rates for O III

    Science.gov (United States)

    Tayal, S. S.; Zatsarinny, O.

    2017-12-01

    Transition probabilities, electron excitation collision strengths, and rate coefficients for a large number of O III lines over a broad wavelength range, from the infrared to ultraviolet, have been reported. The collision strengths have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method in combination with B-spline expansions is employed for an accurate representation of the target wave functions. The close-coupling expansion contains 202 O2+ fine-structure levels of the 2{s}22{p}2,2s2{p}3, 2{p}4,2{s}22p3s,3p,3d, 4s,4p,4d,4f,5s, and 2s2{p}33s,3p,3d configurations. The effective collision strengths are obtained by averaging electron excitation collision strengths over a Maxwellian distribution of velocities at electron temperatures ranging from 100 to 100,000 K. The calculated effective collision strengths have been reported for the 20,302 transitions between all 202 fine-structure levels. There is an overall good agreement with the recent R-matrix calculations by Storey et al. for the transitions between all levels of the ground 2{s}22{p}2 configuration, but significant discrepancies have been found with Palay et al. for transitions to the 2{s}22{p}2 1 S 0 level. Line intensity ratios between the optical lines arising from the 2{s}22{p}2{}3{P}{0,1,2} - 1 D 2 transitions have been compared with other calculations and observations from the photoionized gaseous nebulae, and good agreement is found. The present calculations provide the most complete and accurate data sets, which should allow a more detailed treatment of the available measured spectra from different ground and space observatories.

  3. Electron-electron interaction effects on the optical excitations of single-walled carbon nanotubes

    Science.gov (United States)

    Mazumdar, Sumit

    2005-03-01

    We report correlated-electron calculations of optically excited states in ten semiconducting single-walled carbon nanotubes (SWCNTs) with a wide range of diameters.ootnotetextHongbo Zhao and Sumit Mazumdar, Phys. Rev. Lett. 93, 157402 (2004) First, we show that optical excitation in SWCNTs occurs to excitons whose binding energies decrease with the increasing nanotube diameter, and are smaller than the binding energy of an isolated strand of poly-(paraphenylenevinylene), (PPV). Second, electron-electron interactions split the degeneracies characteristic of cylindrical geometries, and in all cases there occur forbidden excitons below the optical exciton. We ascribe the experimentally observed low quantum efficiency of the photoluminescence of SWCNTs to the presence of these forbidden states. Third, while within one-electron theory the transverse photo-excitations occur exactly halfway between the two lowest longitudinally polarized absorptions, they are shifted to considerably above the central region for nonzero electron-electron interactions. Finally, the ratio of the threshold energy of the second longitudinally polarized optical absorption to that of the lowest such transition in the widest SWCNTs is less than 2 within correlated-electron theory, in agreement with experiments.

  4. Low-energy electron scattering from molecules, biomolecules and surfaces

    CERN Document Server

    Carsky, Petr

    2011-01-01

    Since the turn of the 21st century, the field of electron molecule collisions has undergone a renaissance. The importance of such collisions in applications from radiation chemistry to astrochemistry has flowered, and their role in industrial processes such as plasma technology and lighting are vital to the advancement of next generation devices. Furthermore, the development of the scanning tunneling microscope highlights the role of such collisions in the condensed phase, in surface processing, and in the development of nanotechnology.Low-Energy Electron Scattering from Molecules, Biomolecule

  5. Electron-vibron coupling effects on electron transport via a single-molecule magnet

    NARCIS (Netherlands)

    McCaskey, A.; Yamamoto, Y.; Warnock, M.; Burzuri, E.; Van der Zant, H.S.J.; Park, K.

    2015-01-01

    We investigate how the electron-vibron coupling influences electron transport via an anisotropic magnetic molecule, such as a single-molecule magnet (SMM) Fe4, by using a model Hamiltonian with parameter values obtained from density-functional theory (DFT). The magnetic anisotropy parameters,

  6. Integral cross sections for electron impact excitation of vibrational and electronic states in phenol

    Energy Technology Data Exchange (ETDEWEB)

    Neves, R. F. C. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Instituto Federal do Sul de Minas Gerais, Campus Poços de Caldas, Minas Gerais (Brazil); Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, Minas Gerais (Brazil); Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Lopes, M. C. A. [Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, Minas Gerais (Brazil); Blanco, F. [Departamento de Física Atómica, Molecular y Nuclear, Universidad Complutense de Madrid, 28040 Madrid (Spain); García, G. [Instituto de Física Fundamental, CSIC, Serrano 113-bis, 28006 Madrid (Spain); Ratnavelu, K. [Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Brunger, M. J., E-mail: Michael.Brunger@flinders.edu.au [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2015-05-21

    We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of composite vibrational modes and electronic-states in phenol, where the energy range of those experiments was 15–250 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely, for the inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. In addition, for the relevant dipole-allowed excited electronic states, we also report f-scaled Born-level and energy-corrected and f-scaled Born-level (BEf-scaled) ICS. Where possible, our measured and calculated ICSs are compared against one another with the general level of accord between them being satisfactory to within the measurement uncertainties.

  7. Mode coupling and multiquantum vibrational excitations in Feshbach-resonant positron annihilation in molecules

    Science.gov (United States)

    Gribakin, G. F.; Stanton, J. F.; Danielson, J. R.; Natisin, M. R.; Surko, C. M.

    2017-12-01

    The dominant mechanism of low-energy positron annihilation in polyatomic molecules is through positron capture in vibrational Feshbach resonances (VFR). In this paper, we investigate theoretically the effect of anharmonic terms in the vibrational Hamiltonian on positron annihilation rates. Such interactions enable positron capture in VFRs associated with multiquantum vibrational excitations, leading to enhanced annihilation. Mode coupling can also lead to faster depopulation of VFRs, thereby reducing their contribution to the annihilation rates. To analyze this complex picture, we use coupled-cluster methods to calculate the anharmonic vibrational spectra and dipole transition amplitudes for chloroform, chloroform-d1, 1,1-dichloroethylene, and methanol, and use these data to compute positron resonant annihilation rates for these molecules. Theoretical predictions are compared with the annihilation rates measured as a function of incident positron energy. The results demonstrate the importance of mode coupling in both enhancement and suppression of the VFR. There is also experimental evidence for the direct excitation of multimode VFR. Their contribution is analyzed using a statistical approach, with an outlook towards more accurate treatment of this phenomenon.

  8. Electron scattering resonances and dissociative attachment in polyatomic molecules

    International Nuclear Information System (INIS)

    Olthoff, J.K.

    1985-01-01

    A relatively new technique, electron transmission spectroscopic, is now being used to investigate the unoccupied valence molecular orbitals of many chemical compounds. Electron-transmission spectroscopy measures the energy of negative ion states that arise from electron capture into unoccupied molecular orbitals. Additional information about the unoccupied orbitals may be obtained if the negative ion decays by way of dissociation. Determination of the identity, kinetic energy, and production rates of stable ion fragments supplies information about the shape and position of the potential energy curves which describe the electronic states of the molecule and the anion. Used together, photoelectron, electron transmission, and dissociation data can produce a complete picture of a molecule's valence electronic structure. For this work, a time-of-flight mass spectrometer was attached to an electron transmission spectrometer to observe negative ion fragments due to dissociative attachment. The mass spectrometer measures the identify and kinetic energy of stable negative ions as a function of incident electron energy. Electron transmission spectra and ion production data were acquired for many compounds in four chemical categories

  9. Electronic structure, spectra, and nature of electronically excited states of the bifluorophores stilbene-CH2-coumarine and phenyl-CH2-coumarine

    Science.gov (United States)

    Sokolova, I. V.; Vasil'Eva, N. Yu.; Vylegzhanina, Ya. O.; Maier, G. V.

    1993-09-01

    Quantum-chemical calculations of trans-stilbene and benzene molecules as well as molecules of bifluorophores based on them — trans-stilbene-CH2-coumarine 120 and phenyl-CH2-coumarine — were performed by the INDO/S method. The form of the molecular orbitals, the distribution of the electron density in the ground and excited states, the spectra and nature of the electronically states of bifluorophore molecules were established in relation to the energy donor and acceptor molecules. Three conformations of the bifluorophore molecules were studied (planar, “edge,” “wing”). It was discovered that the energy and type of the molecular orbitals of the bifluorophores are independent of the relative orientation of the donor and acceptor subsystems. It is shown that the mixed character of the three lowest electronically excited states, participating in the formation of the spectrum, of the bifluorophores gives rise to quite appreciable overlapping of their electronic wave functions and, therefore, ensures that the internal-conversion processes are efficient.

  10. First Principles Calculations of Electronic Excitations in 2D Materials

    DEFF Research Database (Denmark)

    Rasmussen, Filip Anselm

    Since the first reported synthesization of graphene ̣- an atomically thin carbon material - in 2004 there has been a surge of research in discovering other novel two-dimensional materials. The reason is clear: two-dimensional materials are thought to be able to lead to new fast and low-power ultra...... mechanics methods. One of these methods, Density Functional Theory (DFT), has been very successful at determining structural properties of 2D materials. It is however well-known that it less accurate when it comes to predicting the energy levels of excited states that are important in order to determine...... of the numerical methods that are efficient for bulk systems become invalid. In this thesis I describe the study of a set of novel 2D materials and establish their electronic and optical properties using DFT and the GW approximation while taking the reduced screening properly into account as well as taking regard...

  11. Development of neutral beam source using electron beam excited plasma

    International Nuclear Information System (INIS)

    Hara, Yasuhiro; Hamagaki, Manabu; Mise, Takaya; Hara, Tamio

    2011-01-01

    A low-energy neutral beam (NB) source, which consists of an electron-beam-excited plasma (EBEP) source and two carbon electrodes, has been developed for damageless etching of ultra-large-scale integrated (ULSI) devices. It has been confirmed that the Ar ion beam energy was controlled by the acceleration voltage and the beam profile had good uniformity over the diameter of 80 mm. Dry etching of a Si wafer at the floating potential has been carried out by Ar NB. Si sputtering yield by an Ar NB clearly depends on the acceleration voltage. This result shows that the NB has been generated through the charge exchange reaction from the ion beam in the process chamber. (author)

  12. Electronically excited states of carbazole-modified ortho-phenylenes

    Science.gov (United States)

    Muraoka, Azusa; Fukabori, Nao

    2018-02-01

    In recent years new materials for phosphorescent organic light-emitting diodes were found from complexes of carbazole-modified ortho-phenylene derivatives. We investigate theoretically the photo-induced charge transfer in these complexes. The electronically excited states and absorption spectra of tetramer ortho-phenylene (OP) derivatives were first studied by using time-dependent density functional theory calculations with various functionals. The functional that best reproduced the experimental results was found to be ωB97XD, and the assignment of the experimentally observed ultraviolet-visible absorption spectrum was successfully performed in comparison with the theoretically obtained one. We then performed a spectral assignment of carbazole-modified OP derivatives.

  13. Electron Transport in Quantum Dots and Heat Transport in Molecules

    DEFF Research Database (Denmark)

    Kirsanskas, Gediminas

    to make a device in order to get fundamentally new properties?” [1], or more concretely, when do the quantum effects become important. During the last 30 years, the innovations in fabrication and cooling techniques allowed to produce nanometer scale solid-state or single molecule-based devices......, electrically confined electrons in semiconductor nanowires, two dimensional electron gases, carbon nanotubes, or just small metallic particles, nanoscale pieces of semiconductor....

  14. Quasiclassical R-matrix theory of inelastic processes in collisions of electrons with HCl molecules

    International Nuclear Information System (INIS)

    Fabrikant, I.I.

    1991-01-01

    The R-matrix theory for the vibrational excitation and dissociative attachment in e-HCl collisions is developed. Only one pole in the R-matrix expansion is included. This allows for making a connection between the R-matrix and the nonlocal-complex-potential theories, and for obtaining the expression for the dissociative-attachment cross section without using the R-matrix radius in the internuclear coordinate. All matrix elements in the equation for the vibrational-excitation and dissociative-attachment amplitudes are calculated using the quasiclassical approach. We study how the results depend on the number of vibrational levels of the neutral molecule included in the theory and show how to exclude the vibrational continuum by a modification of the nonlocal-complex potential. The results for the vibrational-excitation cross sections are extremely sensitive to the behavior of the R-matrix potential curve near the point of crossing this curve with the potential curve of the neutral molecule. Particularly in some cases the cross section at the threshold peak exhibits the boomerang oscillations earlier found for HCl by Domcke [in Aspects of Electron-Molecule Scattering and Photoionization, edited by A. Herzenberg (AIP, New Haven, 1989), p. 169]. The dissociative-attachment cross sections are in reasonable agreement with experiment and with other theories

  15. Towards first-principles calculation of electronic excitations in the ring of the protein-bound bacteriochlorophylls

    Science.gov (United States)

    Polyakov, Igor V.; Khrenova, Maria G.; Moskovsky, Alexander A.; Shabanov, Boris M.; Nemukhin, Alexander V.

    2018-04-01

    Modeling electronic excitation of bacteriochlorophyll (BChl) molecules in light-harvesting (LH) antennae from photosynthetic centers presents a challenge for the quantum theory. We report on a quantum chemical study of the ring of 32 BChl molecules from the bacterial core complex LH1-RC. Diagonal and off-diagonal elements of the excitonic Hamiltonian matrices are estimated in quantum chemical calculations of relevant fragments using the TD-DFT and CIS approaches. The deviation of the computed excitation energy of this BChl system from the experimental data related to the Qy band maximum of this LH1-RC complex is about 0.2 eV. We demonstrate that corrections due to improvement in modeling of an individual BChl molecule and due to contributions from the protein environment are in the range of the obtained discrepancy between theory and experiment. Differences between results of the excitonic model and direct quantum chemical calculations of BChl aggregates fall in the same range.

  16. Ab initio design of picosecond infrared laser pulses for controlling vibrational-rotational excitation of CO molecules

    Science.gov (United States)

    Herrmann, Thomas; Ren, Qinghua; Balint-Kurti, Gabriel G.; Manby, Frederick R.

    2007-06-01

    Optimal control of rovibrational excitations of the CO molecule using picosecond infrared laser pulses is described in the framework of the electric-nuclear Born-Oppenheimer approximation [G. G. Balint-Kurti et al., J. Chem. Phys. 122, 084110 (2005)]. The potential energy surface of the CO molecule in the presence of an electric field is calculated using coupled cluster theory with a large orbital basis set. The quantum dynamics of the process is treated using a full three dimensional treatment of the molecule in the laser field. The detailed mechanisms leading to efficient control of the selected excitation processes are discussed.

  17. Electron excitation cross sections for some Ar I 5d (J = 2) levels

    International Nuclear Information System (INIS)

    Blanco, F.; Sanchez, J.A.; Campos, J.

    1992-01-01

    Absolute excitation cross sections by electron impact for some 5d levels with J = 2 of Ar I have been measured by the optical method. Excitation functions for electron energies in the range from the excitation threshold to 1000 eV are also reported. A delayed coincidence analysis of the de-excitation at 100 eV electron energy allowed for the subtraction of radiative cascades. The resulting excitation cross sections are between 7.3 and 12x10 -20 cm 2 . (author)

  18. Behavior of ro-vibrationally excited H2 molecules and H atoms in a plasma expansion

    International Nuclear Information System (INIS)

    Vankan, P.; Schram, D.C.; Engeln, R.

    2005-01-01

    The behavior in a supersonic plasma expansion of H atom and H2 molecules, both ground-state and ro-vibrationally excited, is studied using various laser spectroscopic techniques. The ground-state H2 molecules expand like a normal gas. The behavior of H atoms and H 2 rv molecules, on the other hand, is considerably influenced, and to some extend even determined, by their reactivity. The H atoms diffuse out of the expansion due to surface association at the walls of the vacuum vessel. Moreover, by reducing the surface area of the nozzle by a factor of two, the amount of H atoms leaving the source is increased by one order of magnitude, due to a decreased surface association of H atoms in the nozzle. The evolution of the ro-vibrational distributions along the expansion axis shows the relaxation of the molecular hydrogen from the high temperature in the up-stream region to the low ambient temperature in the down-stream region. Whereas the vibrational distribution resembles a Boltzmann distribution, the rotational distribution is a non-equilibrium one, in which the high rotational levels (J > 7) are much more populated than what is expected from the low rotational levels (J <5). We observed overpopulations of up to seven orders of magnitude. The production of the high rotational levels is very probably connected to the surface association in the nozzle

  19. Do vibrationally excited OH molecules affect middle and upper atmospheric chemistry?

    Directory of Open Access Journals (Sweden)

    T. von Clarmann

    2010-10-01

    Full Text Available Except for a few reactions involving electronically excited molecular or atomic oxygen or nitrogen, atmospheric chemistry modelling usually assumes that the temperature dependence of reaction rates is characterized by Arrhenius' law involving kinetic temperatures. It is known, however, that in the upper atmosphere the vibrational temperatures may exceed the kinetic temperatures by several hundreds of Kelvins. This excess energy has an impact on the reaction rates. We have used upper atmospheric OH populations and reaction rate coefficients for OH(v=0...9+O3 and OH(v=0...9+O to estimate the effective (i.e. population weighted reaction rates for various atmospheric conditions. We have found that the effective rate coefficient for OH(v=0...9+O3 can be larger by a factor of up to 1470 than that involving OH in its vibrational ground state only. At altitudes where vibrationally excited states of OH are highly populated, the OH reaction is a minor sink of Ox and O3 compared to other reactions involving, e.g., atomic oxygen. Thus the impact of vibrationally excited OH on the ozone or Ox sink remains small. Among quiescent atmospheres under investigation, the largest while still small (less than 0.1% effect was found for the polar winter upper stratosphere and mesosphere. The contribution of the reaction of vibrationally excited OH with ozone to the OH sink is largest in the upper polar winter stratosphere (up to 4%, while its effect on the HO2 source is larger in the lower thermosphere (up to 1.5% for polar winter and 2.5% for midlatitude night conditions. For OH(v=0...9+O the effective rate coefficients are lower by up to 11% than those involving OH in its vibrational ground state. The effects on the odd oxygen sink are negative and can reach −3% (midlatitudinal nighttime lowermost thermosphere, i.e. neglecting vibrational excitation overestimates the odd

  20. Transport coefficients in high-temperature ionized air flows with electronic excitation

    Science.gov (United States)

    Istomin, V. A.; Oblapenko, G. P.

    2018-01-01

    Transport coefficients are studied in high-temperature ionized air mixtures using the modified Chapman-Enskog method. The 11-component mixture N2/N2+/N /N+/O2/O2+/O /O+/N O /N O+/e- , taking into account the rotational and vibrational degrees of freedom of molecules and electronic degrees of freedom of both atomic and molecular species, is considered. Using the PAINeT software package, developed by the authors of the paper, in wide temperature range calculations of the thermal conductivity, thermal diffusion, diffusion, and shear viscosity coefficients for an equilibrium ionized air mixture and non-equilibrium flow conditions for mixture compositions, characteristic of those in shock tube experiments and re-entry conditions, are performed. For the equilibrium air case, the computed transport coefficients are compared to those obtained using simplified kinetic theory algorithms. It is shown that neglecting electronic excitation leads to a significant underestimation of the thermal conductivity coefficient at temperatures higher than 25 000 K. For non-equilibrium test cases, it is shown that the thermal diffusion coefficients of neutral species and the self-diffusion coefficients of all species are strongly affected by the mixture composition, while the thermal conductivity coefficient is most strongly influenced by the degree of ionization of the flow. Neglecting electronic excitation causes noticeable underestimation of the thermal conductivity coefficient at temperatures higher than 20 000 K.

  1. Cotunneling spectroscopy and the properties of excited-state spin manifolds of Mn12 single molecule magnets

    Science.gov (United States)

    Rostamzadeh Renani, Fatemeh; Kirczenow, George

    2014-10-01

    We study charge transport through single molecule magnet (SMM) junctions in the cotunneling regime as a tool for investigating the properties of the excited-state manifolds of neutral Mn12 SMs. This study is motivated by a recent transport experiment [S. Kahle et al., Nano Lett. 12, 518 (2012), 10.1021/nl204141z] that probed the details of the magnetic and electronic structure of Mn12 SMMs beyond the ground-state spin manifold. A giant spin Hamiltonian and master equation approach is used to explore theoretically the cotunneling transport through Mn12-Ac SMM junctions. We identify SMM transitions that can account for both the strong and weak features of the experimental differential conductance spectra. We find the experimental results to imply that the excited spin-state manifolds of the neutral SMM have either different anisotropy constants or different g factors in comparison with its ground-state manifold. However, the latter scenario accounts best for the experimental data.

  2. Excited states

    CERN Document Server

    Lim, Edward C

    1974-01-01

    Excited States, Volume I reviews radiationless transitions, phosphorescence microwave double resonance through optical spectra in molecular solids, dipole moments in excited states, luminescence of polar molecules, and the problem of interstate interaction in aromatic carbonyl compounds. The book discusses the molecular electronic radiationless transitions; the double resonance techniques and the relaxation mechanisms involving the lowest triplet state of aromatic compounds; as well as the optical spectra and relaxation in molecular solids. The text also describes dipole moments and polarizab

  3. Electronic interaction between nitrogen-doped graphene and porphyrin molecules.

    Science.gov (United States)

    Pham, Van Dong; Lagoute, Jérôme; Mouhoub, Ouafi; Joucken, Frédéric; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie

    2014-09-23

    The chemical doping of graphene is a promising route to improve the performances of graphene-based devices through enhanced chemical reactivity, catalytic activity, or transport characteristics. Understanding the interaction of molecules with doped graphene at the atomic scale is therefore a leading challenge to be overcome for the development of graphene-based electronics and sensors. Here, we use scanning tunneling microscopy and spectroscopy to study the electronic interaction of pristine and nitrogen-doped graphene with self-assembled tetraphenylporphyrin molecules. We provide an extensive measurement of the electronic structure of single porphyrins on Au(111), thus revealing an electronic decoupling effect of the porphyrins adsorbed on graphene. A tip-induced switching of the inner hydrogen atoms of porphyrins, first identified on Au(111), is observed on graphene, allowing the identification of the molecular conformation of porphyrins in the self-assembled molecular layer. On nitrogen-doped graphene, a local modification of the charge transfer around the nitrogen sites is evidenced via a downshift of the energies of the molecular elecronic states. These data show how the presence of nitrogen atoms in the graphene network modifies the electronic interaction of organic molecules with graphene. These results provide a basic understanding for the exploitation of doped graphene in molecular sensors or nanoelectronics.

  4. Search fot Excited Electrons with ATLAS at LHC: Z,W decay channels.

    CERN Document Server

    Cakir, O; Mehdiyev, R

    2002-01-01

    We study excited electrons production at the CERN LHC through contact interactions and the subsequent decays to ordinary electrons and gauge bosons via gauge interactions. Decay widths exhanced by contact interactions are also examined. Excited electrons can be accessible up to a mass range of 500 GeV - 3 TeV.

  5. The Dynamics of Dissociative Electron Attachment to Small Polyatomic Molecules

    Science.gov (United States)

    Rescigno, Thomas

    2013-09-01

    Dissociative electron attachment (DEA) is a resonant process in which an electron attaches to a molecule to form an unstable anion which subsequently fragments into stable products. DEA to small polyatomic molecules is often governed by complex electronic and nuclear dynamics that is intrinsically multi-dimensional. One-dimensional treatments of the dissociation dynamics based on resonance scattering theory, while often successful in modeling the energy dependence of total cross sections, can mask the complexity of post-attachment dynamics which is revealed by the observed angular dependence of the reaction products. The dissociation evolves on transient anion potential energy surfaces and often involves conical intersections which can result in a complete breakdown of the axial recoil approximation. I will use the examples of DEA to water, carbon dioxide and methanol to illustrate the discussion. Work performed under auspices of USDOE by LBNL under contract DE-AC02-05CH11231 and supported by OBES, Division of Chemical Sciences.

  6. Quantum-Sequencing: Fast electronic single DNA molecule sequencing

    Science.gov (United States)

    Casamada Ribot, Josep; Chatterjee, Anushree; Nagpal, Prashant

    2014-03-01

    A major goal of third-generation sequencing technologies is to develop a fast, reliable, enzyme-free, high-throughput and cost-effective, single-molecule sequencing method. Here, we present the first demonstration of unique ``electronic fingerprint'' of all nucleotides (A, G, T, C), with single-molecule DNA sequencing, using Quantum-tunneling Sequencing (Q-Seq) at room temperature. We show that the electronic state of the nucleobases shift depending on the pH, with most distinct states identified at acidic pH. We also demonstrate identification of single nucleotide modifications (methylation here). Using these unique electronic fingerprints (or tunneling data), we report a partial sequence of beta lactamase (bla) gene, which encodes resistance to beta-lactam antibiotics, with over 95% success rate. These results highlight the potential of Q-Seq as a robust technique for next-generation sequencing.

  7. Electronic band structure in porous silicon studied by photoluminescence and photoluminescence excitation spectroscopy

    International Nuclear Information System (INIS)

    Lee, Ki-Won; Kim, Young-You

    2004-01-01

    In this research, we used photoluminescence (PL) and photoluminescence excitation (PLE) to visualize the electronic band structure in porous silicon (PS). From the combined results of the PLE measurements at various PL emission energies and the PL measurements under excitation at various PLE absorption energies, we infer that three different electronic band structures, originating from different luminescent origins, give rise to the PL spectrum. Through either thermal activation or diffusive transfer, excited carriers are moved to each of the electronic band structures.

  8. Analytic approximations for integrated electron-atom excitations

    International Nuclear Information System (INIS)

    McCarthy, I.E.; Saha, B.C.; Stelbovics, A.T.

    1980-09-01

    Accurate calculations of atomic excitations require estimates of the effect of higher excitations on the effective (optical) potential coupling various reaction channels. The total cross section for a particular excitation is proportional to the maximum contribution of that excitation to the imaginary part of the elastic momentum-space optical potential, and is typical of the contribution to the potential in general. Analytic expressions relevant to the calculation of optical potentials are given. Their validity is estimated by comparison with more-accurate calculations and with experimental excitation cross sections

  9. Electron-phonon relaxation and excited electron distribution in gallium nitride

    Energy Technology Data Exchange (ETDEWEB)

    Zhukov, V. P. [Institute of Solid State Chemistry, Urals Branch of the Russian Academy of Sciences, Pervomayskaya st. 91, Yekaterinburg (Russian Federation); Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tyuterev, V. G., E-mail: valtyut00@mail.ru [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tomsk State Pedagogical University, Kievskaya st. 60, Tomsk (Russian Federation); Tomsk State University, Lenin st. 36, Tomsk (Russian Federation); Chulkov, E. V. [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tomsk State University, Lenin st. 36, Tomsk (Russian Federation); Departamento de Fisica de Materiales, Facultad de Ciencias Qumicas, UPV/EHU and Centro de Fisica de Materiales CFM-MPC and Centro Mixto CSIC-UPV/EHU, Apdo. 1072, 20080 San Sebastian (Spain); Echenique, P. M. [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Qumicas, UPV/EHU and Centro de Fisica de Materiales CFM-MPC and Centro Mixto CSIC-UPV/EHU, Apdo. 1072, 20080 San Sebastian (Spain)

    2016-08-28

    We develop a theory of energy relaxation in semiconductors and insulators highly excited by the long-acting external irradiation. We derive the equation for the non-equilibrium distribution function of excited electrons. The solution for this function breaks up into the sum of two contributions. The low-energy contribution is concentrated in a narrow range near the bottom of the conduction band. It has the typical form of a Fermi distribution with an effective temperature and chemical potential. The effective temperature and chemical potential in this low-energy term are determined by the intensity of carriers' generation, the speed of electron-phonon relaxation, rates of inter-band recombination, and electron capture on the defects. In addition, there is a substantial high-energy correction. This high-energy “tail” largely covers the conduction band. The shape of the high-energy “tail” strongly depends on the rate of electron-phonon relaxation but does not depend on the rates of recombination and trapping. We apply the theory to the calculation of a non-equilibrium distribution of electrons in an irradiated GaN. Probabilities of optical excitations from the valence to conduction band and electron-phonon coupling probabilities in GaN were calculated by the density functional perturbation theory. Our calculation of both parts of distribution function in gallium nitride shows that when the speed of the electron-phonon scattering is comparable with the rate of recombination and trapping then the contribution of the non-Fermi “tail” is comparable with that of the low-energy Fermi-like component. So the high-energy contribution can essentially affect the charge transport in the irradiated and highly doped semiconductors.

  10. Ozone kinetics in low-pressure discharges: vibrationally excited ozone and molecule formation on surfaces

    International Nuclear Information System (INIS)

    Marinov, Daniil; Guaitella, Olivier; Booth, Jean-Paul; Rousseau, Antoine; Guerra, Vasco

    2013-01-01

    A combined experimental and modeling investigation of the ozone kinetics in the afterglow of pulsed direct current discharges in oxygen is carried out. The discharge is generated in a cylindrical silica tube of radius 1 cm, with short pulse durations between 0.5 and 2 ms, pressures in the range 1–5 Torr and discharge currents ∼40–120 mA. Time-resolved absolute concentrations of ground-state atoms and ozone molecules were measured simultaneously in situ, by two-photon absorption laser-induced fluorescence and ultraviolet absorption, respectively. The experiments were complemented by a self-consistent model developed to interpret the results and, in particular, to evaluate the roles of vibrationally excited ozone and of ozone formation on surfaces. It is found that vibrationally excited ozone, O 3 * , plays an important role in the ozone kinetics, leading to a decrease in the ozone concentration and an increase in its formation time. In turn, the kinetics of O 3 * is strongly coupled with those of atomic oxygen and O 2 (a 1 Δ g ) metastables. Ozone formation at the wall does not contribute significantly to the total ozone production under the present conditions. Upper limits for the effective heterogeneous recombination probability of O atoms into ozone are established. (paper)

  11. Ozone kinetics in low-pressure discharges: vibrationally excited ozone and molecule formation on surfaces

    Science.gov (United States)

    Marinov, Daniil; Guerra, Vasco; Guaitella, Olivier; Booth, Jean-Paul; Rousseau, Antoine

    2013-10-01

    A combined experimental and modeling investigation of the ozone kinetics in the afterglow of pulsed direct current discharges in oxygen is carried out. The discharge is generated in a cylindrical silica tube of radius 1 cm, with short pulse durations between 0.5 and 2 ms, pressures in the range 1-5 Torr and discharge currents ˜40-120 mA. Time-resolved absolute concentrations of ground-state atoms and ozone molecules were measured simultaneously in situ, by two-photon absorption laser-induced fluorescence and ultraviolet absorption, respectively. The experiments were complemented by a self-consistent model developed to interpret the results and, in particular, to evaluate the roles of vibrationally excited ozone and of ozone formation on surfaces. It is found that vibrationally excited ozone, O_3^{*} , plays an important role in the ozone kinetics, leading to a decrease in the ozone concentration and an increase in its formation time. In turn, the kinetics of O_3^{*} is strongly coupled with those of atomic oxygen and O2(a 1Δg) metastables. Ozone formation at the wall does not contribute significantly to the total ozone production under the present conditions. Upper limits for the effective heterogeneous recombination probability of O atoms into ozone are established.

  12. Nuclear Excitation by Electronic Transition of U-235

    Energy Technology Data Exchange (ETDEWEB)

    Chodash, Perry Adam [Univ. of California, Berkeley, CA (United States)

    2015-07-14

    Nuclear excitation by electronic transition (NEET) is a rare nuclear excitation that is theorized to occur in numerous isotopes. One isotope in particular, 235U, has been studied several times over the past 40 years and NEET of 235U has never been conclusively observed. These past experiments generated con icting results with some experiments claiming to observe NEET of 235U and others setting limits for the NEET rate. This dissertation discusses the latest attempt to measure NEET of 235U. If NEET of 235U were to occur, 235mU would be created. 235mU decays by internal conversion with a decay energy of 76 eV and a half-life of 26 minutes. A pulsed Nd:YAG laser operating at 1064 nm with a pulse energy of 789 mJ and a pulse width of 9 ns was used to generate a uranium plasma. The plasma was captured on a catcher plate and electrons emitted from the catcher plate were accelerated and focused onto a microchannel plate detector. A decay of 26 minutes would suggest the creation of 235mU and the possibility that NEET occurred. However, measurements performed using a variety of uranium targets spanning depleted uranium up to 99.4% enriched uranium did not observe a 26 minute decay. Numerous other decays were observed with half-lives ranging from minutes up to hundreds of minutes. While NEET of 235U was not observed during this experiment, an upper limit for the NEET rate of 235U was determined. In addition, explanations for the con icting results from previous experiments are given. Based on the results of this experiment and the previous experiments looking for NEET of 235U, it is likely that NEET of 235U has never been observed.

  13. Differential electron emission from polycyclic aromatic hydrocarbon molecules under fast ion impact.

    Science.gov (United States)

    Biswas, Shubhadeep; Champion, Christophe; Weck, P F; Tribedi, Lokesh C

    2017-07-17

    Interaction between polycyclic aromatic hydrocarbon (PAH) molecule and energetic ion is a subject of interest in different areas of modern physics. Here, we present measurements of energy and angular distributions of absolute double differential electron emission cross section for coronene (C 24 H 12 ) and fluorene (C 13 H 10 ) molecules under fast bare oxygen ion impact. For coronene, the angular distributions of the low energy electrons are quite different from that of simpler targets like Ne or CH 4 , which is not the case for fluorene. The behaviour of the higher electron energy distributions for both the targets are similar to that for simple targets. In case of coronene, a clear signature of plasmon resonance is observed in the analysis of forward-backward angular asymmetry of low energy electron emission. For fluorene, such signature is not identified probably due to lower oscillator strength of plasmon compared to the coronene. The theoretical calculation based on the first-order Born approximation with correct boundary conditions (CB1), in general, reproduced the experimental observations qualitatively, for both the molecules, except in the low energy region for coronene, which again indicates the role of collective excitation. Single differential and total cross sections are also deduced. An overall comparative study is presented.

  14. Theoretical and experimental differential cross sections for electron impact excitation of the electronic bands of furfural

    Energy Technology Data Exchange (ETDEWEB)

    Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Neves, R. F. C. [Instituto Federal do Sul de Minas Gerais, Câmpus Poços de Caldas, Minas Gerais (Brazil); Departamento de Física, UFJF, Juiz de Fora, Minas Gerais 36036-900 (Brazil); Lopes, M. C. A. [Departamento de Física, UFJF, Juiz de Fora, Minas Gerais 36036-900 (Brazil); Costa, R. F. da [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo 09210-580 (Brazil); Instituto de Física “Gleb Wataghin,” Universidade Estadual de Campinas, Campinas, São Paulo 13083-859 (Brazil); Varella, M. T. do N [Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970 São Paulo (Brazil); Bettega, M. H. F. [Departamento de Física, Universidade Federal do Paraná, CP 19044, Curitiba, Paraná 81531-990 (Brazil); Lima, M. A. P., E-mail: maplima@ifi.unicamp.br [Instituto de Física “Gleb Wataghin,” Universidade Estadual de Campinas, Campinas, São Paulo 13083-859 (Brazil); García, G. [Instituto de Física Fundamental, CSIC, Serrano 113-bis, 28006 Madrid (Spain); and others

    2016-03-28

    We report results from a joint experimental and theoretical investigation into electron scattering from the important industrial species furfural (C{sub 5}H{sub 4}O{sub 2}). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C{sub 5}H{sub 4}O{sub 2}. The measurements were carried out at energies in the range 20–40 eV, and for scattered-electron angles between 10° and 90°. The energy resolution of those experiments was typically ∼80 meV. Corresponding Schwinger multichannel method with pseudo-potential calculations, for energies between 6–50 eV and with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were undertaken at the static exchange plus polarisation-level using a minimum orbital basis for single configuration interaction (MOB-SCI) approach. Agreement between the measured and calculated DCSs was qualitatively quite good, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOB-SCI. The role of multichannel coupling on the computed electronic-state DCSs is also explored in some detail.

  15. Theoretical and experimental differential cross sections for electron impact excitation of the electronic bands of furfural

    International Nuclear Information System (INIS)

    Jones, D. B.; Neves, R. F. C.; Lopes, M. C. A.; Costa, R. F. da; Varella, M. T. do N; Bettega, M. H. F.; Lima, M. A. P.; García, G.

    2016-01-01

    We report results from a joint experimental and theoretical investigation into electron scattering from the important industrial species furfural (C 5 H 4 O 2 ). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C 5 H 4 O 2 . The measurements were carried out at energies in the range 20–40 eV, and for scattered-electron angles between 10° and 90°. The energy resolution of those experiments was typically ∼80 meV. Corresponding Schwinger multichannel method with pseudo-potential calculations, for energies between 6–50 eV and with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were undertaken at the static exchange plus polarisation-level using a minimum orbital basis for single configuration interaction (MOB-SCI) approach. Agreement between the measured and calculated DCSs was qualitatively quite good, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOB-SCI. The role of multichannel coupling on the computed electronic-state DCSs is also explored in some detail.

  16. Excitation and deexcitation of N2 molecular levels. Induced fluorescence by electrons and laser

    International Nuclear Information System (INIS)

    Perez Fernandez-Mayoralas, A.

    1989-01-01

    The electron impact excitation followed by fluorescence induced by N 2 -laser absorption was used to study the lifetime of the lowest vibrational level of the B 3 π g electronic state of N 2 . The experimental result of this work is 13 + 1 μs. To measure the lifetime of B 3 π g (v=2,3,5,6,7,8) levels the delayed coincidence method by electron impact was use. The lifetime values were compared with recent experimental and theoretical results. The relative intensi-ties of 3 π g --- A 3 Σ Ω + system bands, in the range (6540-10500 A o ) was measured using a hollow cathode lamp as spectral source. The relative transition moments and its dependence versus the r-centroid was obtained. Total cross sections for electron scattering by N molecules in the range 600 - 5000 eV have been obtained from measurements of the attenuation of a linear electron beam. The results have been compared with available experimental cross sections and with theoretical calculations based on the first Born approximation. (Author)

  17. Negative ions of polyatomic molecules

    International Nuclear Information System (INIS)

    Christophorou, LG.

    1980-01-01

    In this paper general concepts relating to, and recent advances in, the study of negative ions of polyatomic molecules are discussed with emphasis on halocarbons. The topics dealt with in the paper are as follows: basic electron attachment processes, modes of electron capture by molecules, short-lived transient negative ions, dissociative electron attachment to ground-state molecules and to hot molecules (effects of temperature on electron attachment), parent negative ions, effect of density, nature, and state of the medium on electron attachment, electron attachment to electronically excited molecules, the binding of attached electrons to molecules (electron affinity), and the basic and the applied significance of negative-ion studies

  18. A molecular symmetry analysis of the electronic states and transition dipole moments for molecules with two torsional degrees of freedom

    Energy Technology Data Exchange (ETDEWEB)

    Obaid, R. [Institut für Theoretische Chemie, Universität Wien, Währinger Straße 17, 1090 Vienna (Austria); Applied Chemistry Department, Palestine Polytechnic University, Hebron, Palestine (Country Unknown); Leibscher, M., E-mail: monika.leibscher@itp.uni-hannover.de [Institut für Theoretische Physik, Leibniz Universität Hannover, Appelstr. 2, 30167 Hannover (Germany)

    2015-02-14

    We present a molecular symmetry analysis of electronic states and transition dipole moments for molecules which undergo large amplitude intramolecular torsions. The method is based on the correlation between the point group of the molecule at highly symmetric configurations and the molecular symmetry group. As an example, we determine the global irreducible representations of the electronic states and transition dipole moments for the quinodimethane derivative 2-[4-(cyclopenta-2,4-dien-1-ylidene)cyclohexa-2,5-dien-1-ylidene]-2H-1, 3-dioxole for which two torsional degrees of freedom can be activated upon photo-excitation and construct the resulting symmetry adapted transition dipole functions.

  19. The Role of Electronic Excitations on Chemical Reaction Dynamics at Metal, Semiconductor and Nanoparticle Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tully, John C. [Yale Univ., New Haven, CT (United States)

    2017-06-10

    Chemical reactions are often facilitated and steered when carried out on solid surfaces, essential for applications such as heterogeneous catalysis, solar energy conversion, corrosion, materials processing, and many others. A critical factor that can determine the rates and pathways of chemical reactions at surfaces is the efficiency and specificity of energy transfer; how fast does energy move around and where does it go? For reactions on insulator surfaces energy transfer generally moves in and out of vibrations of the adsorbed molecule and the underlying substrate. By contrast, on metal surfaces, metallic nanoparticles and semiconductors, another pathway for energy flow opens up, excitation and de-excitation of electrons. This so-called “nonadiabatic” mechanism often dominates the transfer of energy and can directly impact the course of a chemical reaction. Conventional computational methods such as molecular dynamics simulation do not account for this nonadiabatic behavior. The current DOE-BES funded project has focused on developing the underlying theoretical foundation and the computational methodology for the prediction of nonadiabatic chemical reaction dynamics at surfaces. The research has successfully opened up new methodology and new applications for molecular simulation. In particular, over the last three years, the “Electronic Friction” theory, pioneered by the PI, has now been developed into a stable and accurate computational method that is sufficiently practical to allow first principles “on-the-fly” simulation of chemical reaction dynamics at metal surfaces.

  20. submitter Measurement of LYSO Intrinsic Light Yield Using Electron Excitation

    CERN Document Server

    Martinez Turtos, Rosana; Pizzichemi, Marco; Ghezzi, Alessio; Pauwels, Kristof; Auffray, Etiennette; Lecoq, Paul; Paganoni, Marco

    2016-01-01

    The determination of the intrinsic light yield $(LY_{int})$ of scintillating crystals, i.e. number of optical photons created per amount of energy deposited, constitutes a key factor in order to characterize and optimize their energy and time resolution. However, until now measurements of this quantity are affected by large uncertainties and often rely on corrections for bulk absorption and surface/edge state. The novel idea presented in this contribution is based on the confinement of the scintillation emission in the central upper part of a 10 mm cubic crystal using a 1.5 MeV electron beam with diameter of 1 mm. A black non-reflective pinhole aligned with the excitation point is used to fix the light extraction solid angle (narrower than total reflection angle), which then sets a light cone travel path through the crystal. The final number of photoelectrons detected using a Hamamatsu R2059 photomultiplier tube (PMT) was corrected for the extraction solid angle, the Fresnel reflection coefficient and quantum...

  1. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    2001-01-01

    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive...... theory of charge transfer in polar media offers convenient tools for the treatment of experimental data for such systems, with due account of large-amplitude strongly anharmonic intramolecular reorganization. Equations for the activation barrier and free energy relationships are provided, incorporating...

  2. Electron scattering from molecules and molecular aggregates of biological relevance

    Science.gov (United States)

    Gorfinkiel, Jimena D.; Ptasinska, Sylwia

    2017-09-01

    In this Topical Review we survey the current state of the art in the study of low energy electron collisions with biologically relevant molecules and molecular clusters. We briefly describe the methods and techniques used in the investigation of these processes and summarise the results obtained so far for DNA constituents and their model compounds, amino acids, peptides and other biomolecules. The applications of the data obtained is briefly described as well as future required developments.

  3. Path-integral approach to resonant electron-molecule scattering

    International Nuclear Information System (INIS)

    Winterstetter, M.; Domcke, W.

    1993-01-01

    A path-integral formulation of resonant electron-molecule scattering is developed within the framework of the projection-operator formalism of scattering theory. The formation and decay of resonances is treated in real time as a quantum-mechanical electronic-tunneling process, modified by the coupling of the electronic motion with the nuclear degrees of freedom. It is shown that the electronic continuum can be summed over in the path-integral formulation, resulting formally in the path integral for an effective two-state system with coupling to vibrations. The harmonic-oscillator approximation is adopted for the vibrational motion in the present work. Approximation methods are introduced which render the numerical evaluation of the sum over paths feasible for up to ∼10 3 elementary time slices. The theory is numerically realized for simple but nontrivial models representing the 2 Π g d-wave shape resonance in e - +N 2 collisions and the 2 Σ u + p-wave shape resonance in e - +H 2 collisions, respectively. The accuracy of the path-integral results is assessed by comparison with exact numerical reference data for these models. The essential virtue of the path-integral approach is the fact that the computational effort scales at most linearly with the number of vibrational degrees of freedom. The path-integral method is thus well suited to treat electron collisions with polyatomic molecules and molecular aggregates

  4. Differential cross sections for electron impact excitation of the electronic bands of phenol

    Energy Technology Data Exchange (ETDEWEB)

    Neves, R. F. C. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Instituto Federal do Sul de Minas Gerais, Campus Poços de Caldas, Minas Gerais (Brazil); Departamento de Física, UFJF, Juiz de Fora, Minas Gerais (Brazil); Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Lopes, M. C. A.; Nixon, K. L. [Departamento de Física, UFJF, Juiz de Fora, Minas Gerais (Brazil); Silva, G. B. da [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Universidade Federal de Mato Grosso, Barra do Garças, Mato Grosso (Brazil); Duque, H. V. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Departamento de Física, UFJF, Juiz de Fora, Minas Gerais (Brazil); Oliveira, E. M. de; Lima, M. A. P. [Instituto de Física “Gleb Wataghin,” Universidade Estadual de Campinas, 13083-859 Campinas, São Paulo (Brazil); Costa, R. F. da [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-580 Santo André, São Paulo (Brazil); Varella, M. T. do N. [Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970 São Paulo (Brazil); Bettega, M. H. F. [Departamento de Física, Universidade Federal do Paraná, CP 19044, 81531-990 Curitiba, Paraná (Brazil); and others

    2015-03-14

    We report results from a joint theoretical and experimental investigation into electron scattering from the important organic species phenol (C{sub 6}H{sub 5}OH). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C{sub 6}H{sub 5}OH. The measurements were carried out at energies in the range 15–40 eV, and for scattered-electron angles between 10{sup ∘} and 90{sup ∘}. The energy resolution of those experiments was typically ∼80 meV. Corresponding Schwinger multichannel method with pseudo-potentials calculations, with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were conducted at the static exchange plus polarisation (SEP)-level using a minimum orbital basis for single configuration interaction (MOBSCI) approach. Agreement between the measured and calculated DCSs was typically fair, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOBSCI.

  5. Chemical physics of molecules and continuous channel electron multipliers

    Science.gov (United States)

    Judge, D. L.

    1971-01-01

    The A approaches X, B approaches X and B approaches A bands of CO(+) have been excited using monochromatic photons and the band intensities measured. Using such data the variations of the electronic transition moments for these above emission bands as well as for the absorption bands have been determined. Further, the specific cross sections for the absorption processes have been determined by measuring the total emission intensity in the band system through which the upper state decays. The band intensity measurements and the derived results are presented.

  6. Electronic excitation of some silicium compounds in the vacuum ultravi olet region

    International Nuclear Information System (INIS)

    Rocco, M.L.M.

    1986-01-01

    Angle-resolved electron energy-loss spectra have been measured for the tetramethylsilane, trimethylchlorosilane and dimethyldichloresilane molecules in the 5 - 300 eV energy range. The spectra have been obtained at 1 KeV incident energy, with an energy resolution of about 0.5 eV (valense region) and 0.8 eV (inner-shell region). Both the valence and core-level excitation bands can be as associated to transitions to Rydber and valence states. No dipole-allowed transition has been observed in the spectra measured in the angular range of 1 to 9 degrees (valence region) and 3 to 7 degrees (inner-shell region). (Author) [pt

  7. Plasmon-mediated electron emission from the coronene molecule under fast ion impact

    Science.gov (United States)

    Biswas, Shubhadeep; Tribedi, L. C.

    2015-12-01

    The existence of the collective electronic excitation in polycyclic aromatic hydrocarbon (PAH) molecules has been predicted before on the basis of the presence of a large delocalized π electron cloud around the carbon skeleton. Here, we present a manifestation of energy and angular distributions of electron emission upon deexcitation of the collective plasmon resonance in coronene, a PAH molecule, under fast ion impact. The angular distributions of these electrons show an unusually enhanced forward-backward angular asymmetry, in contrast to the observed uniform distributions for simpler atomic (Ne) or molecular (CH4) targets. A simple model of photoelectron angular distribution from an oscillating dipolar plasmon, calculated including the first retardation term in the transition matrix element, provides excellent agreement with the observed distribution. The ratio of forward-to-backward electron emission intensity clearly exhibits a broad peak which is in excellent agreement with the theoretical prediction of the plamson peak. This observation may provide some new inputs towards the astrophysical problem of UV photon absorption by PAHs in the interstellar medium, or in the search for materials suitable for UV plasmonics.

  8. Theoretical research of electron-ion direct impact excitation cross sections for hot dense plasma

    International Nuclear Information System (INIS)

    Tian Mingfeng

    2003-01-01

    An average-atom (AA) model, Younger formula and partial wave method are employed to study the electron- ion direct impact excitation cross sections for hot dense plasma. The phenomenon of electron resonance near the excitation threshold and its mechanism are discussed. (author)

  9. Effect of vacuum polarization on the excitation of hydrogen atom by electron impact

    Directory of Open Access Journals (Sweden)

    Sujata Bhattacharyya

    1981-01-01

    for 1S−2S excitation of the hydrogen atom by electron impact. The excitation amplitude calculated field theoretically is found to be lowered by 0.47t2/(t2+93 where t2=4|P−Q|2, P and Q being the momenta of the incident and scattered electrons respectively.

  10. Huygens-Fresnel picture for electron-molecule elastic scattering★

    Science.gov (United States)

    Baltenkov, Arkadiy S.; Msezane, Alfred Z.

    2017-11-01

    The elastic scattering cross sections for a slow electron by C2 and H2 molecules have been calculated within the framework of the non-overlapping atomic potential model. For the amplitudes of the multiple electron scattering by a target the wave function of the molecular continuum is represented as a combination of a plane wave and two spherical waves generated by the centers of atomic spheres. This wave function obeys the Huygens-Fresnel principle according to which the electron wave scattering by a system of two centers is accompanied by generation of two spherical waves; their interaction creates a diffraction pattern far from the target. Each of the Huygens waves, in turn, is a superposition of the partial spherical waves with different orbital angular momenta l and their projections m. The amplitudes of these partial waves are defined by the corresponding phases of electron elastic scattering by an isolated atomic potential. In numerical calculations the s- and p-phase shifts are taken into account. So the number of interfering electron waves is equal to eight: two of which are the s-type waves and the remaining six waves are of the p-type with different m values. The calculation of the scattering amplitudes in closed form (rather than in the form of S-matrix expansion) is reduced to solving a system of eight inhomogeneous algebraic equations. The differential and total cross sections of electron scattering by fixed-in-space molecules and randomly oriented ones have been calculated as well. We conclude by discussing the special features of the S-matrix method for the case of arbitrary non-spherical potentials. Contribution to the Topical Issue "Low energy positron and electron interactions", edited by James Sullivan, Ron White, Michael Bromley, Ilya Fabrikant, and David Cassidy.

  11. Zeeman effect in the IR spectrum of a molecule without an electronic moment

    International Nuclear Information System (INIS)

    Koloshnikov, V.G.; Kuritsyn, Yu.A.; Pak, I.; Ulitskiy, N.I.; Kharlamov, B.M.; Britov, A.D.; Zasavitsky, I.I.; Shotov, A.P.

    1980-01-01

    The Zeeman effect in the infrared absorption spectrum of a molecule without an electronic magnetic moment was observed using a linear spectroscopic technique with a tunable diode laser. In the magnetic field B = 500 kG weak splittings of the asR(4,1) and asR(4,0) lines in the ν 2 -band of NH 3 were recorded. The values of the Zeeman splittings in these cases were approx. 1 x 1 10 -2 cm -1 . The picture of the Zeeman splittings observed is shown to be connected with the difference between the g-factors for the excited (ν 2 = 1) and the ground (ν 2 = 0) vibrational states of the NH 3 molecule. This difference is about (-10)-(15)% of the g-factor for the lower vibrational level of the transition. (orig.)

  12. Theoretical studies of inelastic molecule-surface and resonant electron-atom and electron-molecule scattering

    International Nuclear Information System (INIS)

    Mowrey, R.C. Jr.

    1985-01-01

    In part I, two problems in the inelastic scattering of molecules from nonvibrating surfaces are discussed. First, the close coupling (CC) method is used to study the orientational dependence of the transition probabilities for vibrationally and rotationally inelastic scattering of H 2 and N 2 from flat surfaces. The dependence of vibrational transition probabilities on the orientation of the molecule is strong but decreases as the energy increases. Second, a new approximation to the CC method for treating scattering of molecules from corrugated surfaces is discussed. The proposed local normal model of j/sub z/ conservation assumes that the component of the rotational angular momentum of the incident molecule which is parallel to the normal to the surface at the impact point is conserved during a collision. In part II, the use of the complex basis function method to study two shape resonances in electron scattering is discussed. The complex self-consistent-field (CSCF) method was used to obtain the position and width of the 2 D shape resonance in electron-calcium scattering. Comparison with experimental results shows that the lifetime is influenced by correlation effects. The CSCF and complex configuration interaction (CCI) methods were used to obtain the complex potential energy function for nuclear motion for the 2 Σ/sub u/ + resonance state of H 2 -

  13. Theoretical study of Raman chirped adiabatic passage by X-ray absorption spectroscopy: Highly excited electronic states and rotational effects

    Energy Technology Data Exchange (ETDEWEB)

    Engin, Selma [Sorbonne Universités, UPMC Univ Paris 06, UMR 7614, Laboratoire de Chimie Physique Matière et Rayonnement, F-75005 Paris (France); CNRS, UMR 7614, Laboratoire de Chimie Physique Matière et Rayonnement, F-75005 Paris (France); Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049 Madrid (Spain); Sisourat, Nicolas, E-mail: Nicolas.Sisourat@upmc.fr; Selles, Patricia; Taïeb, Richard; Carniato, Stéphane [Sorbonne Universités, UPMC Univ Paris 06, UMR 7614, Laboratoire de Chimie Physique Matière et Rayonnement, F-75005 Paris (France); CNRS, UMR 7614, Laboratoire de Chimie Physique Matière et Rayonnement, F-75005 Paris (France)

    2014-06-21

    Raman Chirped Adiabatic Passage (RCAP) is an efficient method to climb the vibrational ladder of molecules. It was shown on the example of fixed-in-space HCl molecule that selective vibrational excitation can thus be achieved by RCAP and that population transfer can be followed by X-ray Photoelectron spectroscopy [S. Engin, N. Sisourat, P. Selles, R. Taïeb, and S. Carniato, Chem. Phys. Lett. 535, 192–195 (2012)]. Here, in a more detailed analysis of the process, we investigate the effects of highly excited electronic states and of molecular rotation on the efficiency of RCAP. Furthermore, we propose an alternative spectroscopic way to monitor the transfer by means of X-ray absorption spectra.

  14. Simultaneous Evaluation of Multiple Rotationally Excited States of Floppy Molecules Using Diffusion Monte Carlo

    Science.gov (United States)

    McCoy, Anne B.; Ford, Jason E.; Marlett, Melanie L.; Petit, Andrew S.

    2014-06-01

    In this work, an extension to diffusion Monte Carlo (DMC) is proposed, allowing for the simultaneous calculation of the energy and wave function of multiple rotationally excited states of floppy molecules. The total wave function is expanded into a set of Dirac δ-functions called walkers, while the rotational portion of the wave function is expanded in a symmetric top basis set. Each walker is given a rotational state vector containing coefficients for all states of interest. The positions of the atoms and the coefficients in the state vector evolve according to the split operator approximation of the quantum propagator. The method was benchmarked by comparing calculated rotation-vibration energies for H_3^+, H_2D^+, and H_3O^+ to experimental values. For low to moderate values of J, the resulting energies are within the statistical uncertainty of the calculation. Rotation-vibration coupling is captured through flexibility introduced in the form of the vibrational wave function. This coupling is found to increase with increasing J-values. Based on the success achieved through these systems, the method was applied to CH_5^+ and its deuterated isotopologues for v = 0, J ≥ 10. Based on these calculations, the energy level structure of CH_5^+ is found to resemble that for a of a spherical top, and excitations up to J = 10 displayed insignificant rotation-vibration coupling. Extensions of this approach that explicitly account for vibrations will also be discussed. ` A. S. Petit, J. E. Ford and A. B. McCoy, J. Phys. Chem. A, in press, K. D. Jordan Festschrift, DOI: 10.1021/jp408821a

  15. Effect of vibrational excitation on the dynamics of ion-molecule reactions

    International Nuclear Information System (INIS)

    Anderson, S.L.

    1981-11-01

    A new experimental technique for the study of vibrational effects on ion-molecule reaction cross sections is described. Vibrational and collision energy dependent cross sections are presented for proton and H atom transfer, charge transfer and collision induced dissociation reactions in various isotopic H 2 + + H 2 systems. Charge and proton transfer cross sections are presented for the reactions of H 2 + and D 2 + with Ar, N 2 , CO, and O 2 . All the reactions are shown to be highly influenced by avoided crossings between the ground and first excited potential energy surfaces. Because of the nature of the crossings, vibrational motion of the systems can cause both adiabatic and non-adiabatic behavior of the system. This makes the vibrational dependences of the various cross sections a very sensitive probe of the dynamics of the collisions particularly, their behavior in the region of the crossings. Evidence is seen for charge transfer between reagents as they approach each other, transition to and in some cases reactions on excited potential energy surfaces, competition between different channels, and strong coupling of proton and charge transfer channels which occurs only for two of the systems studied (H 2 + + Ar, N 2 ). Oscillatory structure is observed in the collision energy dependence of the endoergic H 2 + (v = 0) + Ar charge transfer reaction for the first time, and a simple model which is commonly used for atom-atom charge transfer is used to fit the peaks. Finally a simple model is used to assess the importance of energy resonance and Franck-Condon effects on molecular charge transfer

  16. Study of electron impact inelastic scattering of chlorine molecule (Cl2)

    Science.gov (United States)

    Yadav, Hitesh; Vinodkumar, Minaxi; Limbachiya, Chetan; Vinodkumar, P. C.

    2018-02-01

    A theoretical study is carried out for electron interactions with the chlorine molecule (Cl2) for incident energies ranging from 0.01 to 5000 eV. This wide range of energy has allowed us to investigate a variety of processes and report data on symmetric excitation energies, dissociative electron attachment (DEA), total excitation cross sections, and ionization cross section (Q ion) along with total inelastic cross sections (Q inel). The present study is important since Cl2 is a prominent gas for plasma etching and its anionic atoms are important in the etching of semiconductor wafers. In order to compute the total inelastic cross sections, we have employed the ab initio R-matrix method (0.01 to 15 eV) together with the spherical complex optical potential method (∼15 to 5000 eV). The R-matrix calculations are performed using a close coupling method, and we have used DEA estimator via Quantemol-N to calculate the DEA fragmentation and cross sections. The present study finds overall good agreement with the available experimental data. Total excitation and inelastic cross sections of e-{{{Cl}}}2 scattering for a wide energy range (0.01 to 5 keV) are reported for the first time, to the best of our knowledge.

  17. Nonadiabatic electron dynamics in the exit channel of Na-molecule optical collisions.

    Science.gov (United States)

    Rebentrost, F; Figl, C; Goldstein, R; Hoffmannn, O; Spelsberg, D; Grosser, J

    2008-06-14

    We study optical collisions of Na atoms with N(2), CO, C(2)H(2), and CO(2) molecules in a crossed-beam experiment. Excited electronic states of the collision complex are selectively populated during the collision. We measure the relative population of the Na(3p) fine-structure levels after the collision and observe in this way the nonadiabatic transitions occuring in the final phase of the collision process. For the NaCO, NaC(2)H(2), and NaCO(2) systems new ab initio potential surfaces were generated. The theoretical analysis of the nonadiabatic electron dynamics on the excited potential surfaces is made within the classical-path formalism. The results are in good qualitative agreement with the experimental data and provide insight into the nonadiabatic mechanisms prevailing during the evolution in the upper 3p manifold. The differences between the different collisional systems are related to the presence and system-specific locations of conical intersections and avoided crossing seams in the excited potential surfaces.

  18. Induction of unidirectional π-electron rotations in low-symmetry aromatic ring molecules using two linearly polarized stationary lasers.

    Science.gov (United States)

    Mineo, Hirobumi; Yamaki, Masahiro; Kim, Gap-Sue; Teranishi, Yoshiaki; Lin, Sheng Hsien; Fujimura, Yuichi

    2016-09-29

    A new laser-control scenario of unidirectional π-electron rotations in a low-symmetry aromatic ring molecule having no degenerate excited states is proposed. This scenario is based on dynamic Stark shifts of two relevant excited states using two linearly polarized stationary lasers. Each laser is set to selectively interact with one of the two electronic states, the lower and higher excited states are shifted up and down with the same rate, respectively, and the two excited states become degenerate at their midpoint. One of the four control parameters of the two lasers, i.e. two frequencies and two intensities, determines the values of all the other parameters. The direction of π-electron rotations, clockwise or counter-clockwise rotation, depends on the sign of the relative phase of the two lasers at the initial time. An analytical expression for the time-dependent expectation value of the rotational angular momentum operator is derived using the rotating wave approximation (RWA). The control scenario depends on the initial condition of the electronic states. The control scenario with the ground state as the initial condition was applied to toluene molecules. The derived time-dependent angular momentum consists of a train of unidirectional angular momentum pulses. The validity of the RWA was checked by numerically solving the time-dependent Schrödinger equation. The simulation results suggest an experimental realization of the induction of unidirectional π-electron rotations in low-symmetry aromatic ring molecules without using any intricate quantum-optimal control procedure. This may open up an effective generation method of ring currents and current-induced magnetic fields in biomolecules such as amino acids having aromatic ring molecules for searching their interactions.

  19. Electron scattering on molecules: search for semi-empirical indications

    Science.gov (United States)

    Fedus, Kamil; Karwasz, Grzegorz P.

    2017-06-01

    Reliable cross-sections for electron-molecule collisions are urgently needed for numerical modeling of various processes important from technological point of view. Unfortunately, a significant progress in theory and experiment over the last decade is not usually accompanied by the convergence of cross-sections measured at different laboratories and calculated with different methods. Moreover the most advanced contemporary theories involve such large basis sets and complicated equations that they are not easily applied to each specific molecule for which data are needed. For these reasons the search for semi-empirical indications in angular and energy dependencies of scattering cross-section becomes important. In this paper we make a brief review of the applicability of the Born-dipole approximation for elastic, rotational, vibrational and ionization processes that can occur during electron-molecule collisions. We take into account the most recent experimental findings as the reference points. Contribution to the Topical Issue "Atomic and Molecular Data and Their Applications", edited by Gordon W.F. Drake, Jung-Sik Yoon, Daiji Kato, and Grzegorz Karwasz.

  20. Development and implementation of theoretical methods for the description of electronically core-excited states

    Energy Technology Data Exchange (ETDEWEB)

    Wenzel, Jan

    2016-03-23

    -cc-series, a mean error of -0.23% ±0.12% for core-excitation energies can be identified at the CVS-ADC(2)-x level for carbon, nitrogen and oxygen K-edge excitations, whereas CVS-ADC(3) exhibits errors of 0.61% ± 0.32%. This is due to fortuitous error compensation of basis set truncation, electron correlation, orbital relaxation and neglect of relativistic effects at the CVS-ADC(2)-x level. Transition moments and spectral features, as well as static dipole moments, are excellently described with both CVS-ADC(2)-x and CVS-ADC(3). Especially the 6-311++G** basis set provides an excellent ratio of accuracy to computational time. Another important topic is the description of orbital relaxation effects. In the scope of this thesis, I show, how these effects are included indirectly within the CVS-ADC approaches. For this purpose, two different descriptors are used, i.e. electron promotion numbers and the amount of doubly excited amplitudes. Furthermore, with the help of detachment/attachment (D/A) densities, which can be constructed via the CVS-ISR approach, relaxation effects can be visualized. For this purpose, the (D/A) densities are compared with hole/electron (h/e) densities based on the transition density matrix. With this knowledge, the X-ray absorption spectra of medium-sized molecules and radicals from the fields of organic electronics and biology are investigated and analyzed. On the basis of these studies, the restricted and unrestricted versions of CVS-ADC(2)-x in combination with the 6-311++G** basis set exhibit mean errors of core-excitation energies around 0.1%, compared to experimental values. Additionally, core-excited state characters are analyzed with the help of state densities obtained via the CVS-ISR approach or the transition density matrix. To demonstrate the computational savings as a function of the size of the core space, several systems are investigated. CVS-ADC(3) calculations take about 8-10 times longer than CVS-ADC(2)-x calculations and since the

  1. Free electrons and ionic liquids: study of excited states by means of electron-energy loss spectroscopy and the density functional theory multireference configuration interaction method.

    Science.gov (United States)

    Regeta, Khrystyna; Bannwarth, Christoph; Grimme, Stefan; Allan, Michael

    2015-06-28

    The technique of low energy (0-30 eV) electron impact spectroscopy, originally developed for gas phase molecules, is applied to room temperature ionic liquids (IL). Electron energy loss (EEL) spectra recorded near threshold, by collecting 0-2 eV electrons, are largely continuous, assigned to excitation of a quasi-continuum of high overtones and combination vibrations of low-frequency modes. EEL spectra recorded by collecting 10 eV electrons show predominantly discrete vibrational and electronic bands. The vibrational energy-loss spectra correspond well to IR spectra except for a broadening (∼0.04 eV) caused by the liquid surroundings, and enhanced overtone activity indicating a contribution from resonant excitation mechanism. The spectra of four representative ILs were recorded in the energy range of electronic excitations and compared to density functional theory multireference configuration interaction (DFT/MRCI) calculations, with good agreement. The spectra up to about 8 eV are dominated by π-π* transitions of the aromatic cations. The lowest bands were identified as triplet states. The spectral region 2-8 eV was empty in the case of a cation without π orbitals. The EEL spectrum of a saturated solution of methylene green in an IL band showed the methylene green EEL band at 2 eV, indicating that ILs may be used as a host to study nonvolatile compounds by this technique in the future.

  2. Quenching of excited uranyl ion during its photochemical reduction with triphenyl-phosphine : Part IV - effect of heterocyclic molecules

    International Nuclear Information System (INIS)

    Sidhu, M.S.; Bhatia, P.V.K.

    1994-01-01

    The presence of heterocyclic compounds triggers off a competition between photophysical and photochemical annihilation of excited uranyl ion during its photochemical reduction with triphenylphosphine. This competition is used to measure Stern-Volmer constant using UV visible spectrophotometer for quenching the uranyl ion luminescence with a number of heterocyclic molecules viz., pyridine, thiophene bipyridyl, tetrahydrofuran and piperidine. (author). 7 refs., 2 figs., 1 tab

  3. Electron and positron collisions with polar molecules: studies with the benchmark water molecule

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Rui; Tennyson, Jonathan [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Faure, Alexandre [Laboratoire d' Astrophysique, UMR 5571 CNRS, Universite Joseph-Fourier, BP 53, 38041 Grenoble cedex 09 (France)], E-mail: j.tennyson@ucl.ac.uk

    2009-07-15

    It is difficult to measure low-energy cross sections for collisions of charged particles with strongly dipolar systems since the magnitude of such cross sections is completely dominated by collisions in the forward direction. Theoretically, it is possible to account for the strong forward scattering using the Born approximation but the procedure for combining Born 'top-up' with the more sophisticated treatments required to treat the scattering in other directions is not unique. This comment describes recent progress in describing both electron and positron collisions with polar molecules taking the important water molecule as a benchmark. Previous calculations on electron water at collision energies below 7 eV are compared with new experiments. Positron water studies up to 10 eV are re-analysed based on given experimental acceptance profiles, which depend on the details of the apparatus and method used in the measurements. It is suggested that theory is capable of giving reliable results for elastic and rotationally inelastic electron/positron collisions with strongly dipolar species.

  4. Formation of cold molecules through the photo-association of cold atoms of Cesium. Existence of long range forces between between cold excited atoms of Cesium

    International Nuclear Information System (INIS)

    Comparat, D.

    1999-09-01

    This thesis deals with the experimental study and the theoretical interpretation of the processes involved in photo-association and the formation of cold caesium molecules. It also presents a study of the dipolar forces between a pair of cold excited caesium atoms. We present here the first photo-association experiment on cold caesium atoms: two cold atoms absorb a photon to form an excited electronically excited molecules in a rotation-vibration level. The first production of cold molecules which was realised experimentally, after the spontaneous deexcitation of the photo-associated molecules, is described, stressing the role of the potential well of the molecular states O g - (6s+6p 3/2 ) or 1 u (6s+6p 3/2 ) of caesium. The detection of the formed caesium molecules is based on a two-photons resonant ionisation that creates Cs 2 + ions, afterwards selectively detected. Temperatures around 20-200 μK have been measured. The photo-associative spectroscopy is described on the theoretical point of view: a detailed theoretical study allows to calculate precisely the asymptotic parts of the potential curves. On the experimental point of view, we present the spectroscopy of the extern potential well of the caesium state O g - (6s+6p 3/2 ) and the construction of an effective potential curve of the RKR type. A unified theory of photo-association in weak field, considered as a collision assisted by laser, is developed. The cold atoms experiments allow to study and control the collision between two atoms whose mutual interaction is of the dipole-dipole type. Two different physical systems are studied: a sample of Rydberg atoms, and the photo-association process which is a laser-assisted collision. A modification of the motion of one pair of atoms makes it possible to control the bipolar forces and to choose the atoms relative speeds. (author)

  5. Electronic states and nature of bonding of the molecule PdGe by all electron ab initio HF–CI calculations and mass spectrometric equilibrium experiments

    DEFF Research Database (Denmark)

    Shim, Irene; Kingcade, Joseph E. , Jr.; Gingerich, Karl A.

    1986-01-01

    In the present work we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of six electronic states of the PdGe molecule. The molecule is predicted to have a 3Pi ground state and two low-lying excited states 3Sigma− and 1Sigma+. The electronic structure...... with a small charge transfer from the Pd to the Ge atom. The dissociation energy of the PdGe molecule has been determined from the mass spectrometric equilibrium data combined with the theoretical results as D00 =252.0±10.5 kJ mol−1. The Journal of Chemical Physics is copyrighted by The American Institute...

  6. Limitations of superfluid helium droplets as host system revealed by electronic spectroscopy of embedded molecules

    Energy Technology Data Exchange (ETDEWEB)

    Premke, Tobias

    2016-02-19

    Superfluid helium nanodroplets serve a unique cryogenic host system ideal to prepare cold molecules and clusters. Structures as well as dynamic processes can be examined by means of high resolution spectroscopy. Dopant spectra are accompanied by helium-induced spectroscopic features which reveal information on the dopant to helium interaction. For this reason the experimental research focuses on the investigation of such helium-induced effects in order to provide new information on the microsolvation inside the droplets. Since the quantitative understanding of helium-induced spectral features is essential to interpret molecular spectra recorded in helium droplets, this study contributes further experimental details on microsolvation in superfluid helium droplets. For this purpose two contrary systems were examined by means of high resolution electronic spectroscopy. The first one, phthalocyanine (Pc), is a planar organic molecule offering a huge and planar surface to the helium atoms and thus, the non-superfluid helium solvation layer can form different structures. The second system is iodine and in contrast to Pc it is of simple molecular shape. That means that in this case different complex structures of the non-superfluid helium solvation layer and the dopant can be expected to be avoided. Thus, both molecules should show clear differences in their microsolvation behavior. In this work a detailed examination of different spectroscopic properties of phthalocyanine is given by means of fluorescence excitation and dispersed emission spectroscopy. It raises legitimate doubts about the assignment of experimentally observed signals to features predicted by the model of the microsolvation. Even though there are no experimental observations which disprove the empirical model for the solvation in helium droplets, an unambiguous assignment of the helium-induced spectroscopic structures is often not possible. In the second part of this work, the investigation of the

  7. Production of excited electrons at TESLA and CLIC based egamma colliders

    CERN Document Server

    Kirca, Z; Cakir, O

    2003-01-01

    We analyze the potential of TESLA and CLIC based electron-photon colliders to search for excited spin-1/2 electrons. The production of excited electrons in the resonance channel through the electron- photon collision and their subsequent decays to leptons and electroweak gauge bosons are investigated. We study in detail the three signal channels of excited electrons and the corresponding backgrounds through the reactions egamma yields egamma, egamma yields eZ and egamma yields vW. Excited electrons with masses up to about 90% of the available collider energy can be probed down to the coupling f = f prime = 0.05(0.1) at TESLA(CLIC) based egamma colliders. 22 Refs.

  8. Parent state swapping of resonances in electron-hydrogen molecule scattering

    International Nuclear Information System (INIS)

    Stibbe, D.T.

    1997-01-01

    Ab initio R-matrix scattering calculations are presented for electron-H 2 as a function of H 2 bond length. It is found that 2 Σ u + and 2Π u resonances in the 10 eV region appear to be associated with multiple 'parent' target states and that the resonances can swap parents as a function of internuclear separation. It is shown how these phenomena provide an explanation for the inconsistencies in previous assignments of resonances in this region and other anomalies such as pronounced isotopic effects. It is suggested that this parent swapping behaviour is likely to be a common feature of electron-impact excitation of other molecules and is particularly important for any models that include nuclear motion. (author)

  9. Investigation of electronically excited indole relaxation dynamics via photoionization and fragmentation pump-probe spectroscopy

    Science.gov (United States)

    Godfrey, T. J.; Yu, Hui; Ullrich, Susanne

    2014-07-01

    The studies herein investigate the involvement of the low-lying 1La and 1Lb states with 1ππ* character and the 1πσ* state in the deactivation process of indole following photoexcitation at 201 nm. Three gas-phase, pump-probe spectroscopic techniques are employed: (1) Time-resolved photoelectron spectroscopy (TR-PES), (2) hydrogen atom (H-atom) time-resolved kinetic energy release (TR-KER), and (3) time-resolved ion yield (TR-IY). Each technique provides complementary information specific to the photophysical processes in the indole molecule. In conjunction, a thorough examination of the electronically excited states in the relaxation process, with particular focus on the involvement of the 1πσ* state, is afforded. Through an extensive analysis of the TR-PES data presented here, it is deduced that the initial excitation of the 1Bb state decays to the 1La state on a timescale beyond the resolution of the current experimental setup. Relaxation proceeds on the 1La state with an ultrafast decay constant (IY experiments, both specifically probing 1πσ* dynamics, exhibit similar decay constants, further validating these observations.

  10. Quantum electrodynamics with nonrelativistic sources. V. Electromagnetic field correlations and intermolecular interactions between molecules in either ground or excited states

    International Nuclear Information System (INIS)

    Power, E.A.; Thirunamachandran, T.

    1993-01-01

    Spatial correlations between electromagnetic fields arising from neutral sources with electric-dipole transition moments are calculated using nonrelativistic quantum electrodynamics in the multipolar formalism. Expressions for electric-electric, magnetic-magnetic, and electric-magnetic correlation functions at two points r and r' are given for a source molecule in either a ground or an excited state. In contrast to the electric-electric and magnetic-magnetic cases there are no electric-magnetic correlations for a ground-state molecule. For an excited molecule the downward transitions contribute additional terms which have modulating factors depending on (r-r')/λ. From these correlation functions electric and magnetic energy densities are found by setting r=r'. These energy densities are then used in a response formalism to calculate intermolecular energy shifts. In the case of two ground-state molecules this leads to the Casimir-Polder potential. However, for a pair of molecules, one or both excited, there are additional terms arising from downward transitions. An important feature of these energies is that they exhibit an R -2 dependence for large intermolecular separations R. This dependence is interpreted in terms of the Poynting vector, which itself can be obtained by setting r=r' in the electric-magnetic correlation function

  11. Electron Correlations and Two-Photon States in Polycyclic Aromatic Hydrocarbon Molecules: A Peculiar Role of Geometry

    OpenAIRE

    Aryanpour, K.; Shukla, A.; Mazumdar, S.

    2013-01-01

    We present numerical studies of one- and two-photon excited states ordering in a number of polycyclic aromatic hydrocarbon molecules: coronene, hexa-peri-hexabenzocoronene and circumcoronene, all possessing $D_{6h}$ point group symmetry versus ovalene with $D_{2h}$ symmetry, within the Pariser-Parr-Pople model of interacting $\\pi$-electrons. The calculated energies of the two-photon states as well as their relative two-photon absorption cross-sections within the interacting model are qualitat...

  12. Excited states v.6

    CERN Document Server

    Lim, Edward C

    1982-01-01

    Excited States, Volume 6 is a collection of papers that discusses the excited states of molecules. The first paper discusses the linear polyene electronic structure and potential surfaces, considering both the theoretical and experimental approaches in such electronic states. This paper also reviews the theory of electronic structure and cites some experimental techniques on polyene excitations, polyene spectroscopic phenomenology, and those involving higher states of polyenes and their triplet states. Examples of these experimental studies of excited states involve the high-resolution one-pho

  13. Excitation energies and properties of open-shell singlet molecules applications to a new class of molecules for nonlinear optics and singlet fission

    CERN Document Server

    Nakano, Masayoshi

    2014-01-01

    This brief investigates the diradical character, which is one of the ground-state chemical indices for 'bond weakness' or 'electron correlation' and which allows researchers to explore the origins of the electron-correlation-driven physico-chemical phenomena concerned with electronic, optical and magnetic properties as well as to control them in the broad fields of physics and chemistry. It then provides the theoretical fundamentals of ground and excited electronic structures of symmetric and asymmetric open-shell molecular systems by using model molecular systems. Moreover, it presents the th

  14. Existence of Hartree-Fock excited states for atoms and molecules

    Science.gov (United States)

    Lewin, Mathieu

    2017-10-01

    For neutral and positively charged atoms and molecules, we prove the existence of infinitely many Hartree-Fock critical points below the first energy threshold (that is, the lowest energy of the same system with one electron removed). This is the equivalent, in Hartree-Fock theory, of the famous Zhislin-Sigalov theorem which states the existence of infinitely many eigenvalues below the bottom of the essential spectrum of the N-particle linear Schrödinger operator. Our result improves a theorem of Lions in 1987 who already constructed infinitely many Hartree-Fock critical points, but with much higher energy. Our main contribution is the proof that the Hartree-Fock functional satisfies the Palais-Smale property below the first energy threshold. We then use minimax methods in the N-particle space, instead of working in the one-particle space.

  15. Exciting: a full-potential all-electron package implementing density-functional theory and many-body perturbation theory.

    Science.gov (United States)

    Gulans, Andris; Kontur, Stefan; Meisenbichler, Christian; Nabok, Dmitrii; Pavone, Pasquale; Rigamonti, Santiago; Sagmeister, Stephan; Werner, Ute; Draxl, Claudia

    2014-09-10

    Linearized augmented planewave methods are known as the most precise numerical schemes for solving the Kohn-Sham equations of density-functional theory (DFT). In this review, we describe how this method is realized in the all-electron full-potential computer package, exciting. We emphasize the variety of different related basis sets, subsumed as (linearized) augmented planewave plus local orbital methods, discussing their pros and cons and we show that extremely high accuracy (microhartrees) can be achieved if the basis is chosen carefully. As the name of the code suggests, exciting is not restricted to ground-state calculations, but has a major focus on excited-state properties. It includes time-dependent DFT in the linear-response regime with various static and dynamical exchange-correlation kernels. These are preferably used to compute optical and electron-loss spectra for metals, molecules and semiconductors with weak electron-hole interactions. exciting makes use of many-body perturbation theory for charged and neutral excitations. To obtain the quasi-particle band structure, the GW approach is implemented in the single-shot approximation, known as G(0)W(0). Optical absorption spectra for valence and core excitations are handled by the solution of the Bethe-Salpeter equation, which allows for the description of strongly bound excitons. Besides these aspects concerning methodology, we demonstrate the broad range of possible applications by prototypical examples, comprising elastic properties, phonons, thermal-expansion coefficients, dielectric tensors and loss functions, magneto-optical Kerr effect, core-level spectra and more.

  16. Experimental electron impact ionization cross sections of molecules for plasma processing

    International Nuclear Information System (INIS)

    Basner, R.; Schmidt, M.; Deutsch, H.; Becker, K.

    2002-01-01

    Non - thermal low temperature plasmas used in plasma processing are mainly composed of hot electrons (average electron energy 0.5 eV - 5 eV), cold ions and neutral gas molecules, which both have energies corresponding to temperatures in the range of 300 K to 1000 K. Electron impact ionization of the neutral heavy particles in ground or in excited states is the initial, and in many plasmas the dominant ion formation process depending on the shape of the electron energy distribution function. The electron impact can produced the molecular ion by direct ionization and by dissociative ionization fragment ions and neutral products such as radicals and smaller neutral stable molecules. An experimental investigation of the formation of molecular positive ions for plasma processing was performed. The ionization cross - section measurements were carried out using a time of flight mass spectrometer under single collision conditions with operating pressures not higher than 0.5 mPa and in linear mode. The ion efficiency curves were measured simultaneously for Ar and the molecule under study in a well defined gas mixture. The measured relative partial ionization cross - sections were put on an absolute scale by normalization relative to the total Ar ionization cross section of 2.77 x 10 - 16 cm 2 at 70 eV. A summary of electron ionization cross - sections results for titanium tetrachloride (TiCl 4 ), tetrafluorosilane (SiF 4 ), and hexafluoroethane (C 2 F 6 ) is presented. Dissociative ionization was found to be the dominant process for all three molecules, there was evidence of the presence of the TiCl 4 + and SiF 4 + parent ions, whereas no ion signals that correspond to the formation of C 2 F 6 + were detected. Only single charged fragment ions ( C 2 F 5 - , C 2 F 4 + , C 2 F + , C 2 - , CF 3 + , CF 2 + , CF - , C + and F - ) from C 2 F 6 were produced, but from TiCl 4 and SiF 4 singly (TiCl x - and SiF x + (x=1-4), Ti + , Cl + ; Si + , F + ) and doubly charged fragment ions

  17. The effect of atoms excited by electron beam on metal evaporation

    CERN Document Server

    Xie Guo Feng; Ying Chun Tong

    2002-01-01

    In atomic vapor laser isotope separation (AVLIS), the metal is heated to melt by electron beams. The vapor atoms may be excited by electrons when flying through the electron beam. The excited atoms may be deexcited by inelastic collision during expansion. The electronic energy transfers translational energy. In order to analyse the effect of reaction between atoms and electron beams on vapor physical parameters, such as density, velocity and temperature, direct-simulation Monte Carlo method (DSMC) is used to simulate the 2-D gadolinium evaporation from long and narrow crucible. The simulation results show that the velocity and temperature of vapor increase, and the density decreases

  18. Excitation and ionic fragmentation of the carvone molecule (C{sub 10}H{sub 14}O) around the O 1s edge

    Energy Technology Data Exchange (ETDEWEB)

    Castilho, R.B. de, E-mail: bobcast@gmail.com [Departamento de Química, Instituto de Ciências Exatas, Universidade Federal do Amazonas (UFAM), Campus Universitário, Coroado, 69077-000 Manaus, AM (Brazil); Nunez, C.V. [Coordenação de Pesquisas em Produtos Naturais, Instituto Nacional de Pesquisas da Amazônia, INPA, 69060-001 Manaus, AM (Brazil); Lago, A.F. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC (UFABC), 09210-170 Santo André, SP (Brazil); Santos, A.C.F.; Coutinho, L.H. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21941-972 Rio de Janeiro, RJ (Brazil); Lucas, C.A. [Instituto de Química, Universidade Federal Fluminense (UFF), 24020150 Rio de Janeiro (Brazil); Pilling, S. [Instituto de Pesquisa e Desenvolvimento (IP and D), Universidade do Vale do Paraíba (UNIVAP), 12244-000 São José dos Campos, SP (Brazil); Silva-Moraes, M.O. [Departamento de Química, Instituto de Ciências Exatas, Universidade Federal do Amazonas (UFAM), Campus Universitário, Coroado, 69077-000 Manaus, AM (Brazil); Souza, G.G.B. de [Instituto de Química, Universidade Federal do Rio de Janeiro (UFRJ), Cidade Universitária, Ilha do Fundão, 21949-900 Rio de Janeiro, RJ (Brazil)

    2014-01-01

    Highlights: • Interaction of the carvone molecule with high energy photons results in an extensive fragmentation of the molecular skeleton. • The occurrence of a site selective mechanism is suggested based on a production of atomic oxygen single and doubly charged, notably around the O 1s edge. • The photoabsorption spectra around O 1s edge present four resonances and the cross section estimation shows a maximum on the first one. - Abstract: The electronic excitation and associated ionic dissociation of the carvone molecule have been studied around the oxygen 1s edge, using synchrotron radiation and time-of-flight techniques. Photoabsorption spectrum (total ion yield) and mass spectra have been obtained in the range between 520 and 545 eV. For the sake of comparison, carvone mass spectra have also been obtained following valence (21.21 eV) and core (carbon 1s) ionization. Fragmentation of the molecule is seen to be greatly enhanced following core excitation. Around the oxygen 1s edge, we observe an extensive fragmentation of the molecular skeleton, as exemplified by the appearance of several previously unreported ions: H{sup +}, H{sub 2}{sup +}, CH{sup +}, CH{sub 2}{sup +} and CH{sub 3}{sup +}, which are not formed at low energies. A maximum is observed at 536 eV photon energy in the relative intensity of the oxygen-containing ions O{sup +}, O{sup 2+} and OH{sup +}, as an evidence for the existence of site-selective fragmentation of the carvone molecule excited around the O 1s edge. Absolute values for the photoionization and photodissociation cross sections were estimated using the molecular additive rule.

  19. Low-energy electron-induced chemistry of condensed methanol: implications for the interstellar synthesis of prebiotic molecules.

    Science.gov (United States)

    Boamah, Mavis D; Sullivan, Kristal K; Shulenberger, Katie E; Soe, ChanMyae M; Jacob, Lisa M; Yhee, Farrah C; Atkinson, Karen E; Boyer, Michael C; Haines, David R; Arumainayagam, Christopher R

    2014-01-01

    In the interstellar medium, UV photolysis of condensed methanol (CH3OH), contained in ice mantles surrounding dust grains, is thought to be the mechanism that drives the formation of "complex" molecules, such as methyl formate (HCOOCH3), dimethyl ether (CH3OCH3), acetic acid (CH3COOH), and glycolaldehyde (HOCH2CHO). The source of this reaction-initiating UV light is assumed to be local because externally sourced UV radiation cannot penetrate the ice-containing dark, dense molecular clouds. Specifically, exceedingly penetrative high-energy cosmic rays generate secondary electrons within the clouds through molecular ionizations. Hydrogen molecules, present within these dense molecular clouds, are excited in collisions with these secondary electrons. It is the UV light, emitted by these electronically excited hydrogen molecules, that is generally thought to photoprocess interstellar icy grain mantles to generate "complex" molecules. In addition to producing UV light, the large numbers of low-energy (methanol, a precursor of several prebiotic species, is the most abundant organic species. Using post-irradiation temperature-programmed desorption, we have investigated the radiolysis initiated by low-energy (7 eV and 20 eV) electrons in condensed methanol at - 85 K under ultrahigh vacuum (5 x 10(-10) Torr) conditions. We have identified eleven electron-induced methanol radiolysis products, which include many that have been previously identified as being formed by methanol UV photolysis in the interstellar medium. These experimental results suggest that low-energy, electron-induced condensed phase reactions may contribute to the interstellar synthesis of "complex" molecules previously thought to form exclusively via UV photons.

  20. Evidence for resonance electron transfer in photon excited X-ray ...

    Indian Academy of Sciences (India)

    with the experimental values and (3) to compare the experimental values obtained by photon excitation with those measured by electron excitation in the available cases. 2. Experimental details. In the present investigations, a Philips 1410 wavelength dispersive plane crystal spectrometer was used. The principle involved ...

  1. The EMP excitation of radiation by the pulsed relativistic electron beam

    International Nuclear Information System (INIS)

    Balakirev, V.A.; Sidelnikov, G.L.

    1996-01-01

    The mechanisms of excitation of ultra-wideband electromagnetic pulses (EMP) by short pulses of high-current relativistic electron beams were proposed and investigated. It is shown that the transformation efficiency of the bunch kinetic energy to the excited energy of the EMP can be very significant. (author). 2 figs., 4 refs

  2. Analytical Hessian of electronic excited states in time-dependent density functional theory with Tamm-Dancoff approximation.

    Science.gov (United States)

    Liu, Jie; Liang, WanZhen

    2011-07-07

    We present the analytical expression and computer implementation for the second-order energy derivatives of the electronic excited state with respect to the nuclear coordinates in the time-dependent density functional theory (TDDFT) with Gaussian atomic orbital basis sets. Here, the Tamm-Dancoff approximation to the full TDDFT is adopted, and therefore the formulation process of TDDFT excited-state Hessian is similar to that of configuration interaction singles (CIS) Hessian. However, due to the replacement of the Hartree-Fock exchange integrals in CIS with the exchange-correlation kernels in TDDFT, many quantitative changes in the derived equations are arisen. The replacement also causes additional technical difficulties associated with the calculation of a large number of multiple-order functional derivatives with respect to the density variables and the nuclear coordinates. Numerical tests on a set of test molecules are performed. The simulated excited-state vibrational frequencies by the analytical Hessian approach are compared with those computed by CIS and the finite-difference method. It is found that the analytical Hessian method is superior to the finite-difference method in terms of the computational accuracy and efficiency. The numerical differentiation can be difficult due to root flipping for excited states that are close in energy. TDDFT yields more exact excited-state vibrational frequencies than CIS, which usually overestimates the values.

  3. Bibliography of electron and photon cross sections with atoms and molecules published in the 20th century. Halogen molecules

    International Nuclear Information System (INIS)

    Hayashi, Makoto

    2003-12-01

    A bibliographies of original and review reports of experiments or theories of electron and photon cross sections and also electron swarm data are presented for atomic or molecular species with specified targets. These works covered 17 atoms and 51 molecules. The present bibliography is only for halogen molecules (F 2 , Cl 2 , Br 2 , I 2 ). About 190(F 2 ), 360(Cl 2 ), 140(Br 2 ) and 240(I 2 ) papers were compiled respectively. A comprehensive author indexes for each molecule are included. The bibliography covers the period 1901 through 2000 for F 2 -I 2 . Finally, author's comments for F 2 -I 2 electron collision cross sections are given. (author)

  4. Bibliography of electron and photon cross sections with atoms and molecules published in the 20th century. Hydrogen halide molecules

    International Nuclear Information System (INIS)

    Hayashi, Makoto

    2004-03-01

    Bibliographies of original and review reports of experiments or theories of electron and photon cross sections and also electron swarm data are presented for atomic or molecular species with specified targets. These works covered 17 atoms and 51 molecules. The present bibliography is only for hydrogen halide molecules (HF, HCL, HBr, HI). About 330 (HF), 420 (HCl) 220 (HBr) and 150 (HI) papers were compiled respectively. Comprehensive author indexes for each molecule are included. The bibliography covers the period 1903 through 2000 for HF-HI. Finally, author's comments for HBr electron collision cross sections are given. (author)

  5. Surface excitations in electron backscattering from silicon surfaces

    Czech Academy of Sciences Publication Activity Database

    Zemek, Josef; Jiříček, Petr; Lesiak, B.; Jablonski, A.

    2004-01-01

    Roč. 562, - (2004), s. 92-100 ISSN 0039-6028 R&D Projects: GA ČR GA202/02/0237 Institutional research plan: CEZ:AV0Z1010914 Keywords : electron-solid interactions * electron-solid scattering and transmission-elastic * electron-solid scattering and transmission-inelastic * Monte Carlo simulation * electron bombardment * silicon Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.168, year: 2004

  6. Modifications of poly (vinilydene fluoride) under electronic excitations produced by charged particles (heavy ions and electrons)

    International Nuclear Information System (INIS)

    Fina, A.

    1990-04-01

    Some of the physico-chemical properties of organic solids like conductivity or permeation can be improved by irradiation. The aim of this work is to characterize modifications induced in poly (vinylidene fluoride) films (PVDF) by charged particles (ions and electrons), with electronic stopping power, for doses ranging from zero to twenty G-Grays. Influence of dose, density of electronic excitations, and flux (in particles per square centimeter), and the nature of defects induced by the beam, were studied with two methods: X-ray Photoelectron Spectroscopy (or XPS) for surface analysis, and electron Spin Resonance (or ESR) to probe the bulk of the film. Three ranges of doses are revealed in view of experimental results. At lower doses, PVDF undergoes deshydrofluorination induced by desorption; it is a low modifications regime. For intermediate range doses, conjugated carbon backbones of polyene compounds are produced. At higher doses, intermolecular interactions between the resulting fragments give a crosslinked network. For the upper limit of doses used, bond breaking results in a non reversible degradation of PVDF. In this last situation, direct atomic displacement of target atoms, is not negligible [fr

  7. An exciton approach to the excited states of two electron atoms. I Formalism and interpretation

    International Nuclear Information System (INIS)

    Schipper, P.E.

    1985-01-01

    The exciton model is formally applied to a description of the excited states of two electron atoms with the explicit inclusion of exchange. The model leads to a conceptually simple framework for the discussion of the electronic properties of the archetypical atomic electron pair

  8. Ultrafast electronic dynamics in laser-excited crystalline bismuth

    Directory of Open Access Journals (Sweden)

    Chekalin S.

    2013-03-01

    Full Text Available Femtosecond spectroscopy was applied to capture complex dynamics of non equilibrium electrons in bismuth. Data analysis reveals significant wavevector dependence of electron-hole and electron-phonon coupling strength along the Γ-T direction of the Brillouin zone

  9. Two-photon-induced hot-electron transfer to a single molecule in a scanning tunneling microscope

    International Nuclear Information System (INIS)

    Wu, S. W.; Ho, W.

    2010-01-01

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photoexcited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron-transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by the polarization measurement. Spatial dependence of the electron-transfer rate exhibits atomic-scale variations. A two-pulse correlation experiment reveals the ultrafast dynamic nature of photoinduced charging process in the STM junction. Results from these experiments are important for understanding photoinduced interfacial charge transfer in many nanoscale inorganic-organic structures.

  10. Reaction of H2 with O2 in Excited Electronic States: Reaction Pathways and Rate Constants.

    Science.gov (United States)

    Pelevkin, Alexey V; Loukhovitski, Boris I; Sharipov, Alexander S

    2017-12-21

    Comprehensive quantum chemical analysis with the use of the multireference state-averaged complete active space self-consistent field approach was carried out to study the reactions of H 2 with O 2 in a 1 Δ g , b 1 Σ g + , c 1 Σ u - , and A' 3 Δ u electronically excited states. The energetically favorable reaction pathways and possible intersystem crossings have been revealed. The energy barriers were refined employing the extended multiconfiguration quasi-degenerate second-order perturbation theory. It has been shown that the interaction of O 2 (a 1 Δ g ) and O 2 (A' 3 Δ u ) with H 2 occurs through the H-abstraction process with relatively low activation barriers that resulted in the formation of the HO 2 molecule in A″ and A' electronic states, respectively. Meanwhile, molecular oxygen in singlet sigma states (b 1 Σ g + and c 1 Σ u - ) was proved to be nonreactive with respect to the molecular hydrogen. Appropriate rate constants for revealed reaction and quenching channels have been estimated using variational transition-state theory including corrections for the tunneling effect, possible nonadiabatic transitions, and anharmonicity of vibrations for transition states and reactants. It was demonstrated that the calculated reaction rate constant for the H 2 + O 2 (a 1 Δ g ) process is in reasonable agreement with known experimental data. The Arrhenius approximations for these processes have been proposed for the temperature range T = 300-3000 K.

  11. Creation and evolution of excited states in anthracene crystals bombarded by electrons

    International Nuclear Information System (INIS)

    Klein, G.

    1978-01-01

    A qualitative description of the kinematics of excited states in anthracene crystals bombarded by electrons is given. It is compared with experimental results concerning scintillation decay curves, and magnetic field effects on the prompt and delayed components of the scintillation

  12. Electron impact excitation of helium in Debye plasma

    Energy Technology Data Exchange (ETDEWEB)

    Diallo, S.; Gomis, L.; Faye, I. G.; Tall, M. S.; Diédhiou, I. [Département de Physique, Faculté des Sciences and Techniques, Université Cheikh Anta Diop, Dakar-Fann (Senegal); Diatta, C. S. [Institut International des Sciences et de Technologie, 28 Avenue des Ambassadeurs Dakar-Fann (Senegal); Zammit, M. [ARC Centre for Antimatter-Matter Studies, Curtin University, GPO Box U1987, Perth, Western Australia 6845 (Australia)

    2015-03-15

    The probability, differential, and integral scattering cross sections of the 1{sup 1}S→2{sup 1}S and 1{sup 1}S→2{sup 1}P transitions of helium have been calculated in the first Born approximation. The projectile-target interactions depending on the temperature and the density of plasma are described by the Debye-Hückel model. Wave functions of the target before and after collision were modeled by non orthogonal Hartree-Fock orbitals. The wave functions parameters are calculated with the Ritz variational method. We improve our unscreened first Born approximation integral cross sections by using the BE-scaled (B stands for binding energy and E excitation energy) method. The second Born approximation has also been used to calculate the excitation cross sections in Debye plasma. Our calculations are compared to other theoretical and experimental results where applicable.

  13. Electronic state selectivity in dication-molecule single electron transfer reactions: NO(2+) + NO.

    Science.gov (United States)

    Parkes, Michael A; Lockyear, Jessica F; Schröder, Detlef; Roithová, Jana; Price, Stephen D

    2011-11-07

    The single-electron transfer reaction between NO(2+) and NO, which initially forms a pair of NO(+) ions, has been studied using a position-sensitive coincidence technique. The reactivity in this class of collision system, which involves the interaction of a dication with its neutral precursor, provides a sensitive test of recent ideas concerning electronic state selectivity in dicationic single-electron transfer reactions. In stark contrast to the recently observed single-electron transfer reactivity in the analogous CO(2)(2+)/CO(2) and O(2)(2+)/O(2) collision systems, electron transfer between NO(2+) and NO generates two product NO(+) ions which behave in an identical manner, whether the ions are formed from NO(2+) or NO. This observed behaviour is in excellent accord with the recently proposed rationalization of the state selectivity in dication-molecule SET reactions using simple propensity rules involving one-electron transitions. This journal is © the Owner Societies 2011

  14. Comparative investigations of the spontaneous and stimulated emissions from nitrogen molecules in air with femtosecond laser excitation pulses

    International Nuclear Information System (INIS)

    Li, Ziting; Wang, Zhanshan; Chu, Wei; Zeng, Bin; Yao, Jinping; Li, Guihua; Xie, Hongqiang; Cheng, Ya

    2016-01-01

    We report on experimental investigations on the spontaneous and stimulated emissions from excited nitrogen molecules generated in both linearly and circularly polarized intense laser fields. The spontaneous emission is measured from the side direction of the laser-induced filament whereas the stimulated emission generated by seed amplification is measured in the forward direction of the laser propagation. The comparison between the signal intensities of the spontaneous fluorescence emission and the seed-amplified stimulated emission provides an insight into the population inversion generated in nitrogen molecules with circularly polarized femtosecond laser pulses. (paper)

  15. New directions in low energy electron molecule collision calculations

    International Nuclear Information System (INIS)

    Burke, P.G.; Noble, C.J.

    1982-01-01

    New theoretical and computational methods for studying low energy electron molecule collisions are discussed. Having considered the fixed-nuclei approximation and the form of the expansion of the total collision wavefunction, the various approximations which have been made are examined, including the static plus model exchange approximation, the static exchange approximation and the close coupling approximation, particular attention being paid to methods of including the molecular charge polarisation. Various ways which have been developed to solve the resultant equations are discussed and it is found that there is increasing emphasis being given to methods which combine the advantages of discrete multi-centre analytic bases with single centre numerical bases. (U.K.)

  16. Nonlinear optical effect and excited electron dynamics of semiconductor nanocrystals; Handotai nano kessh no hisenkei kogaku koka to reiki denshi dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Goto, T. [Tohoku University, Sendai (Japan)

    1996-08-20

    Investigations were given on nanocrystals of CuCl and CdTe with regard to their nonlinear optical mechanism. The experiment used a femto-second pump probe spectroscope. The experiment on CuCl nanocrystals revealed the following facts: in the case where one photon is absorbed into one nanocrystal, cascade mitigation occurs to the pair of electrons and holes, and exciters; and in the case where two photons are absorbed into one nanocrystal, exciter molecules are made via the pair of electrons and holes and the exciters. Thus, it was found that the optical nonlinearity occurs when more than two photons are absorbed into one nanocrystal, and inter-exciter interactions and formation of the exciter molecules are the physical causes thereof. The experiment on CdTe nanocrystals indicated that electrons and holes produced by laser beam are distributed instantaneously between the size-quantized discrete levels, and that temperature in the electron system drops with lapse of time. 9 refs., 6 figs.

  17. Electronic excitations in metallic systems: from defect annihilation to track formation

    International Nuclear Information System (INIS)

    Dunlop, A.; Lesueur, D.

    1991-01-01

    This paper presents an overview of the effects of high electronic energy deposition in metallic targets irradiated with GeV heavy ions. The main result of these investigations is that high electronic excitations lead to various and sometimes conflicting effects according to the nature of the target: - partial annealing of the defects induced by elastic collisions, - creation of additional disorder, - phase transformation (tracks formation and amorphization), - anisotropic growth. These different effects of high electronic energy deposition in metallic targets are probably manifestations at various degrees of the same basic energy transfer process between the excited electrons and the target atoms. Up to now no theoretical model explains these effects. 24 refs

  18. Nonequilibrium Dynamics in a Quasi-Two-Dimensional Electron Plasma after Ultrafast Intersubband Excitation

    International Nuclear Information System (INIS)

    Lutgen, S.; Kaindl, R.A.; Woerner, M.; Elsaesser, T.; Hase, A.; Kuenzel, H.; Gulia, M.; Meglio, D.; Lugli, P.

    1996-01-01

    The dynamics of electrons in GaInAs/AlInAs quantum wells is studied after excitation from the n=1 to the n=2 conduction subband. Femtosecond pump-probe experiments demonstrate for the first time athermal distributions of n=1 electrons on a surprisingly long time scale of 2ps. Thermalization involves intersubband scattering of excited electrons via optical phonon emission with a time constant of 1ps and intrasubband Coulomb and phonon scattering. Ensemble Monte Carlo simulations show that the slow electron equilibration results from Pauli blocking and screening of carrier-carrier scattering. copyright 1996 The American Physical Society

  19. Comparative analysis of the vibrational structure of the absorption spectra of acrolein in the excited ( S 1) electronic state

    Science.gov (United States)

    Koroleva, L. A.; Tyulin, V. I.; Matveev, V. K.; Pentin, Yu. A.

    2012-04-01

    The assignments of absorption bands of the vibrational structure of the UV spectrum are compared with the assignments of bands obtained by the CRDS method in a supersonic jet from the time of laser radiation damping for the trans isomer of acrolein in the excited ( S 1) electronic state. The ν00 trans = 25861 cm-1 values and fundamental frequencies, including torsional vibration frequency, obtained by the two methods were found to coincide in the excited electronic state ( S 1) for this isomer. The assignments of several absorption bands of the vibrational structure of the spectrum obtained by the CRDS method were changed. Changes in the assignment of (0-v') transition bands of the torsional vibration of the trans isomer in the Deslandres table from the ν00 trans trans origin allowed the table to be extended to high quantum numbers v'. The torsional vibration frequencies up to v' = 5 were found to be close to the frequencies found by analyzing the vibrational structure of the UV spectrum and calculated quantum-mechanically. The coincidence of the barrier to internal rotation (the cis-trans transition) in the one-dimensional model with that calculated quantum-mechanically using the two-dimensional model corresponds to a planar structure of the acrolein molecule in the excited ( S 1) electronic state.

  20. Electron excitation collision strengths for positive atomic ions: a collection of theoretical data

    Energy Technology Data Exchange (ETDEWEB)

    Merts, A.L.; Mann, J.B.; Robb, W.D.; Magee, N.H. Jr.

    1980-03-01

    This report contains data on theoretical and experimental cross sections for electron impact excitation of positive atomic ions. It is an updated and corrected version of a preliminary manuscript which was used during an Atomic Data Workshop on Electron Excitation of Ions held at Los Alamos in November 1978. The current status of quantitative knowledge of collisional excitation collision strengths is shown for highly stripped ions where configuration mixing, relativistic and resonance effects may be important. The results show a reasonably satisfactory state for first-row isoelectronic ions and indicate that a considerable amount of work remains to be done for second-row and heavier ions.

  1. Electron-Impact Vibrational Excitation of Polyatomic Gases: Exploratory Caculations

    Czech Academy of Sciences Publication Activity Database

    Cascella, M.; Čurík, Roman; Gianturco, F. A.; Sanna, N.

    2001-01-01

    Roč. 114, č. 5 (2001), s. 1989-2000 ISSN 0021-9606 Institutional research plan: CEZ:AV0Z4040901 Keywords : molecule-scattering * separable approximation * collisions Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.147, year: 2001

  2. Electron collision with the silicon monoxide (SiO) molecule using the R-matrix method

    Energy Technology Data Exchange (ETDEWEB)

    Varambhia, Hemal N; Tennyson, Jonathan [Department of Physics and Astronomy, University College London, Gower St., London WC1E 6BT (United Kingdom); Gupta, Monika; Baluja, K L [Department of Physics and Astrophysics, University of Delhi, Delhi 110007 (India); Faure, Alexandre [Laboratoire d' Astrophysique, UMR 5571 CNRS, Universite Joseph-Fourier, BP 53, 38041 Grenoble Cedex 09 (France)

    2009-05-14

    SiO is a molecule that is well known astrophysically. Electron scattering calculations are presented at the static-exchange and close-coupling approximations, one including 24 target states and another including 48 states. Our study predicts the existence of several low-lying narrow {sup 2}{pi}, {sup 2}{delta} and {sup 2}{sigma}{sup -} Feshbach resonances and confirms the existence of a {sup 2}{pi} bound state. Results from the 48-state close-coupling calculation have been employed to calculate rotational (de)excitation rates and rate-fitting coefficients, which are useful in astrophysical modelling. Ionization cross sections, rotationally summed and resolved differential and integral cross sections are also presented.

  3. Boltzmann equation analysis of electron-molecule collision cross sections in water vapor and ammonia

    International Nuclear Information System (INIS)

    Yousfi, M.; Benabdessadok, M.D.

    1996-01-01

    Sets of electron-molecule collision cross sections for H 2 O and NH 3 have been determined from a classical technique of electron swarm parameter unfolding. This deconvolution method is based on a simplex algorithm using a powerful multiterm Boltzmann equation analysis established in the framework of the classical hydrodynamic approximation. It is well adapted for the simulation of the different classes of swarm experiments (i.e., time resolved, time of flight, and steady state experiments). The sets of collision cross sections that exist in the literature are reviewed and analyzed. Fitted sets of cross sections are determined for H 2 O and NH 3 which exhibit features characteristic of polar molecules such as high rotational excitation collision cross sections. The hydrodynamic swarm parameters (i.e., drift velocity, longitudinal and transverse diffusion coefficients, ionization and attachment coefficients) calculated from the fitted sets are in excellent agreement with the measured ones. These sets are finally used to calculate the transport and reaction coefficients needed for discharge modeling in two cases of typical gas mixtures for which experimental swarm data are very sparse or nonexistent (i.e., flue gas mixtures and gas mixtures for rf plasma surface treatment). copyright 1996 American Institute of Physics

  4. A search for excited electrons with the Compact Muon Solenoid detector

    CERN Document Server

    Dusinberre Sudano, Elizabeth Jane

    2012-01-01

    A search for excited electrons using the CMS detector at the LHC with 36 pb$^{-1}$ of proton-proton collision data recorded at $\\sqrt{s}$ = 7 TeV is presented. The search is performed for associated production of an electron and an excited electron followed by the decay of the excited electron to an electron and a photon for a final state of $ e e \\gamma$. No excess of events above the standard model expectation is observed. Interpreting the results in the context of production via novel four-fermion contact interactions and the subsequent decay via electroweak processes, upper limits on the production cross section are set. The exclusion region in the compositeness scale, $\\Lambda$, and excited electron mass, $M_{e^*}$ , parameter space is extended beyond previously established limits. For $\\Lambda$ = 2 TeV, excited electron masses below 760 GeV/c$^2$ are excluded at the 95% confidence level. The cross sections for masses between 200 and 1500 GeV/c$^2$ are limited to be less than 0.21 - 0.16 pb.

  5. Rate coefficients for reactive elementary processes involving atoms and vibrationally excited molecules

    International Nuclear Information System (INIS)

    Lagana, A.; Ochoa de Aspuru, G.; Riganelli, A.; Garcia, E.

    1996-01-01

    To investigate reactions of atoms with simple molecules with new computation approaches and applying consolidated efficient numerical procedures to the calculation of experimental observables under a wide range of operating conditions were developed. A first family of reactions investigated using the described techniques and computational procedures are those of the nitrogen atom with some diatomic molecules (N 2 and O 2 ) as well as oxygen atom reactions with O 2 and HCl molecules

  6. Electronically driven adsorbate excitation mechanism in femtosecond-pulse laser desorption

    DEFF Research Database (Denmark)

    Brandbyge, Mads; Hedegård, Per; Heinz, T. F.

    1995-01-01

    a systematic theoretical treatment of this coupling process in the language of an electronic friction, which generates Langevin noise in the adsorbate center-of-mass degrees of freedom, while the electronic degrees of freedom are at a high temperature. Starting from an influence-functional path......-integral description, a simple formula for the electronic friction is defined which is valid at all electronic temperatures. At low temperatures the formalism makes contact with the electronic friction appearing in the theory of adsorbate vibrational damping, whereas at high temperatures comparable with the adsorbate...... electronic excitation energies the friction becomes strongly temperature dependent due to dominance by virtual excitations between different adsorbate potential energy surfaces. The former regime is related to the electronic friction model for the desorption process, and the latter to the desorption induced...

  7. Theoretical resonant electron-impact vibrational excitation, dissociative recombination and dissociative excitation cross sections of ro-vibrationally excited BeH+ ion

    International Nuclear Information System (INIS)

    Laporta, V.; Chakrabarti, K.; Celiberto, R.; Janev, R. K.; Mezei, J. Zs.; Niyonzima, S.; Tennyson, J.; Schneider, I.F.

    2017-01-01

    A theoretical study of resonant vibrational excitation, dissociative recombination and dissociative excitation processes of the beryllium monohydride cation, BeH + , induced by electron impact, is reported. Full sets of ro-vibrationally-resolved cross sections and of the corresponding Maxwellian rate coefficients are presented for the three processes. Particular emphasis is given to the high-energy behaviour. Potential curves of 2 σ + , 2 σ and 2 δ symmetries and the corresponding resonance widths, obtained from R-matrix calculations, provide the input for calculations which use a local complex-potential model for resonant collisions in each of the three symmetries. Rotational motion of nuclei and isotopic effects are also discussed. The relevant results are compared with those obtained using a multichannel quantum defect theory method. Full results are available from the Phys4Entry database.

  8. Measurements of electron excitation and recombination for Ne-like Ba46+

    International Nuclear Information System (INIS)

    Marrs, R.E.; Levine, M.A.; Knapp, D.A.; Henderson, J.R.

    1987-07-01

    A new facility at Lawrence Livermore National Laboratory has been used to obtain measurements for electron-impact excitation, dielectronic recombination and radiative recombination for the neon-like Ba 46+ ion. The experimental technique consists of trapping highly charged ions inside the space charge of an electron beam and measuring their x-ray emission spectra

  9. Electron impact excitation collision strengths for neon-like Ni XIX ...

    Indian Academy of Sciences (India)

    presented for electron impact excitation collision strengths for transitions among the fine- structure levels of the ... configuration interaction (CI) as well as relativistic effects in a Breit–Pauli approx- imation. In the present ... among the lowest five levels only, and in a limited range of electron energy above thresholds but below ...

  10. Electron impact excitation of the D states of Mg, Ca and Sr atoms ...

    Indian Academy of Sciences (India)

    electron impact energies of 20 and 40 eV. We compare our results obtained from both the non-relativistic and relativistic methods with each other. Good agreement is found on comparison and the importance of relativistic effects is also explored. Keywords. Electron; excitation; atoms; complete experiment. PACS Nos 34.80.

  11. TARGET EXCITATION IN BARE ION XE/AR COLLISIONS STUDIED BY ELECTRON TARGET ION COINCIDENCES

    NARCIS (Netherlands)

    DENIJS, G; HOEKSTRA, R; MORGENSTERN, R

    We present electron spectra resulting from collisions of bare ions N-15(7+) and C-13(6+) on Ar and the charge state distribution of target ions resulting from C-13(6+)-Xe collisions. From both type of experiments we find evidence that electron capture accompanied by target excitation is an important

  12. Chemical Reactions of Molecules Promoted and Simultaneously Imaged by the Electron Beam in Transmission Electron Microscopy.

    Science.gov (United States)

    Skowron, Stephen T; Chamberlain, Thomas W; Biskupek, Johannes; Kaiser, Ute; Besley, Elena; Khlobystov, Andrei N

    2017-08-15

    The main objective of this Account is to assess the challenges of transmission electron microscopy (TEM) of molecules, based on over 15 years of our work in this field, and to outline the opportunities in studying chemical reactions under the electron beam (e-beam). During TEM imaging of an individual molecule adsorbed on an atomically thin substrate, such as graphene or a carbon nanotube, the e-beam transfers kinetic energy to atoms of the molecule, displacing them from equilibrium positions. Impact of the e-beam triggers bond dissociation and various chemical reactions which can be imaged concurrently with their activation by the e-beam and can be presented as stop-frame movies. This experimental approach, which we term ChemTEM, harnesses energy transferred from the e-beam to the molecule via direct interactions with the atomic nuclei, enabling accurate predictions of bond dissociation events and control of the type and rate of chemical reactions. Elemental composition and structure of the reactant molecules as well as the operating conditions of TEM (particularly the energy of the e-beam) determine the product formed in ChemTEM processes, while the e-beam dose rate controls the reaction rate. Because the e-beam of TEM acts simultaneously as a source of energy for the reaction and as an imaging tool monitoring the same reaction, ChemTEM reveals atomic-level chemical information, such as pathways of reactions imaged for individual molecules, step-by-step and in real time; structures of illusive reaction intermediates; and direct comparison of catalytic activity of different transition metals filmed with atomic resolution. Chemical transformations in ChemTEM often lead to previously unforeseen products, demonstrating the potential of this method to become not only an analytical tool for studying reactions, but also a powerful instrument for discovery of materials that can be synthesized on preparative scale.

  13. Characteristics of Response of Piezoelectric Actuators in Electron Flux Excitation

    Directory of Open Access Journals (Sweden)

    Philip C. Hadinata

    2003-11-01

    Full Text Available In this paper the working parameters of non-contact strain control for piezoelectric ceramics are evaluated. The piezoelectric material functions as an actuator that transforms electrical into mechanical energy, and the electrical input is carried out by electron flux on the positive surface. The sample is exposed to some quasi-static inputs, and its responses are recorded using strain gages. The data shows faster and more stable response in the positive regime, but significantly slower response with drift in the negative regime. An electron collector is introduced on the positive surface to enhance the response in the negative regime. Theoretical analyses of energy transfer and electron movements is discussed, and a string of working conditions for controlling the surface strain of piezoelectric material are given as conclusions.

  14. Bibliography of electron and photon cross sections with atoms and molecules published in the 20th century. Nitrogen molecule

    International Nuclear Information System (INIS)

    Hayashi, Makoto

    2003-06-01

    A bibliography of original and review reports of experiments or theories of electron and photon cross sections and also electron swarm data are presented for atomic or molecular species with specified targets. These works covered 17 atoms and 51 molecules. The present bibliography is only for nitrogen molecule (N 2 ). About 2240 papers were compiled. A comprehensive author index is include. The bibliography covers the period 1906 through 2000 for N 2 . Finally, author's comments for N 2 electron collision cross section are given. (author)

  15. Bibliography of electron and photon cross sections with atoms and molecules published in the 20th century. Hydrogen molecules

    International Nuclear Information System (INIS)

    Hayashi, Makoto

    2004-02-01

    Bibliographies of original and review reports of experiments or theories of electron and photon cross sections and also electron swarm data are presented for atomic or molecular species with specified targets. These works covered 17 atoms and 51 molecules. The present bibliography is only for hydrogen molecules (H 2 , HD, HT, D 2 , DT, T 2 ). About 2200 papers were compiled. A comprehensive author index is included. The bibliography covers the period 1901 through 2000 for H 2 . Finally, author's comments for H 2 electron collision cross sections are given. (author)

  16. Atomic-Scale Control of Electron Transport through Single Molecules

    DEFF Research Database (Denmark)

    Wang, Y. F.; Kroger, J.; Berndt, R.

    2010-01-01

    Tin-phthalocyanine molecules adsorbed on Ag(111) were contacted with the tip of a cryogenic scanning tunneling microscope. Orders-of-magnitude variations of the single-molecule junction conductance were achieved by controllably dehydrogenating the molecule and by modifying the atomic structure...

  17. The interaction of swift electrons with surface excitations

    International Nuclear Information System (INIS)

    Ritchie, R.H.; Tennessee Univ., Knoxville, TN

    1992-01-01

    For many decades swift electrons have comprised a powerful tool for the study of the dynamical properties of condensed matter. The development of this technique has involved much important physics. Here we sketch the historical background of the field and some important developments in theory and experiment. Possible directions for future research are indicated

  18. Quantitative Measurements of Electronically Excited CH Concentration in Normal Gravity and Microgravity Coflow Laminar Diffusion Flames

    Science.gov (United States)

    Giassi, D.; Cao, S.; Stocker, D. P.; Takahashi, F.; Bennett, B. A. V.; Smooke, M. D.; Long, M. B.

    2015-01-01

    With the conclusion of the SLICE campaign aboard the ISS in 2012, a large amount of data was made available for the analysis of the effect of microgravity on laminar coflow diffusion flames. Previous work focused on the study of sooty flames in microgravity as well as the ability of numerical models to predict its formation in a simplified buoyancy-free environment. The current work shifts the investigation to soot-free flames, putting an emphasis on the chemiluminescence emission from electronically excited CH (CH*). This radical species is of significant interest in combustion studies: it has been shown that the electronically excited CH spatial distribution is indicative of the flame front position and, given the relatively simple diagnostic involved with its measurement, several works have been done trying to understand the ability of electronically excited CH chemiluminescence to predict the total and local flame heat release rate. In this work, a subset of the SLICE nitrogen-diluted methane flames has been considered, and the effect of fuel and coflow velocity on electronically excited CH concentration is discussed and compared with both normal gravity results and numerical simulations. Experimentally, the spectral characterization of the DSLR color camera used to acquire the flame images allowed the signal collected by the blue channel to be considered representative of the electronically excited CH emission centered around 431 nm. Due to the axisymmetric flame structure, an Abel deconvolution of the line-of-sight chemiluminescence was used to obtain the radial intensity profile and, thanks to an absolute light intensity calibration, a quantification of the electronically excited CH concentration was possible. Results show that, in microgravity, the maximum flame electronically excited CH concentration increases with the coflow velocity, but it is weakly dependent on the fuel velocity; normal gravity flames, if not lifted, tend to follow the same trend

  19. The influence of autoionizing states on the excitation of helium by electrons

    International Nuclear Information System (INIS)

    Ittersum, T. van

    1976-01-01

    The work described in this thesis deals with resonance effects in the scattering of electrons by helium at energies near the threshold of the autoionizing states (50-70 eV). The investigation is performed by studying light emission following the excitation of singly excited states. In some cases, the polarization of the radiation was also investigated. The purpose of the research was (i) to enlarge our knowledge of triply excited negative ion states, i.e. resonance states which are formed by temporary binding of the incident electron to a doubly excited (autoionizing) state of neutral helium, and (ii) to clear up the nature of some resonance structures which could not be explained in terms of negative ion resonances

  20. The fluorescence and electronic structure of phenyl-substituted tetraazachlorin molecules

    Science.gov (United States)

    Pershukevich, P. P.; Volkovich, D. I.; Gladkov, L. L.; Dudkin, S. V.; Stupak, A. P.; Kuzmitsky, V. A.; Makarova, E. A.; Solovyov, K. N.

    2014-11-01

    The effect of the addition of phenyl groups to pyrrole rings of tetraazachlorins, a new class of tetrapyrroles, on the photophysical properties and electronic structure of the molecules has been investigated by a complex of experimental and theoretical methods. Characteristics of fluorescence at 293 and 77 K have been determined for phenyl-substituted tetraazachlorins. The objects of this study include unsubstituted tetraazaporphine. The introduction of phenyl groups affords a marked increase in the fluorescence quantum yield. For tetraazaporphine and phenyl-substituted tetraazachlorins, fluorescence buildup occurs as the temperature is decreased from 293 to 77 K, but to a lesser extent than for tetraazachlorins having no phenyl groups, which were earlier studied by the authors. The fluorescence buildup mechanism is discussed. The singlet oxygen generation quantum yield has been determined for the tetrapyrroles examined. This characteristic increases upon tetrapyrrole is phenylation. The electronic structure and absorption spectra of unsubstituted porphine and chlorin, tetraazaporphine, tetraazachlorin, octaphenyltetraazaporphine, and tetramethylhexaphenyltetraazachlorin have been calculated by the INDO/Sm method (original modification of the INDO/S method) with molecular geometry optimization using DFT. The results of the quantum-chemical calculation of the absorption spectra are in good agreement with experimental data for transitions to the lowest excited electronic states Q x( S 1) and Q y( S 2).

  1. One-electron densities of freely rotating Wigner molecules

    Science.gov (United States)

    Cioslowski, Jerzy

    2017-12-01

    A formalism enabling computation of the one-particle density of a freely rotating assembly of identical particles that vibrate about their equilibrium positions with amplitudes much smaller than their average distances is presented. It produces densities as finite sums of products of angular and radial functions, the length of the expansion being determined by the interplay between the point-group and permutational symmetries of the system in question. Obtaining from a convolution of the rotational and bosonic components of the parent wavefunction, the angular functions are state-dependent. On the other hand, the radial functions are Gaussians with maxima located at the equilibrium lengths of the position vectors of individual particles and exponents depending on the scalar products of these vectors and the eigenvectors of the corresponding Hessian as well as the respective eigenvalues. Although the new formalism is particularly useful for studies of the Wigner molecules formed by electrons subject to weak confining potentials, it is readily adaptable to species (such as ´balliums’ and Coulomb crystals) composed of identical particles with arbitrary spin statistics and permutational symmetry. Several examples of applications of the present approach to the harmonium atoms within the strong-correlation regime are given.

  2. Determination of ground and excited state dipole moments via electronic Stark spectroscopy: 5-methoxyindole

    Energy Technology Data Exchange (ETDEWEB)

    Wilke, Josefin; Wilke, Martin; Schmitt, Michael, E-mail: mschmitt@uni-duesseldorf.de [Institut für Physikalische Chemie, Heinrich-Heine-Universität, D-40225 Düsseldorf (Germany); Meerts, W. Leo, E-mail: leo.meerts@science.ru.nl [Institute for Molecules and Materials, Radboud University, NL-6525 AS Nijmegen (Netherlands)

    2016-01-28

    The dipole moments of the ground and lowest electronically excited singlet state of 5-methoxyindole have been determined by means of optical Stark spectroscopy in a molecular beam. The resulting spectra arise from a superposition of different field configurations, one with the static electric field almost parallel to the polarization of the exciting laser radiation, the other nearly perpendicular. Each field configuration leads to different intensities in the rovibronic spectrum. With an automated evolutionary algorithm approach, the spectra can be fit and the ratio of both field configurations can be determined. A simultaneous fit of two spectra with both field configurations improved the precision of the dipole moment determination by a factor of two. We find a reduction of the absolute dipole moment from 1.59(3) D to 1.14(6) D upon electronic excitation to the lowest electronically excited singlet state. At the same time, the dipole moment orientation rotates by 54{sup ∘} showing the importance of the determination of the dipole moment components. The dipole moment in the electronic ground state can approximately be obtained from a vector addition of the indole and the methoxy group dipole moments. However, in the electronically excited state, vector addition completely fails to describe the observed dipole moment. Several reasons for this behavior are discussed.

  3. Electron-impact vibrational excitation of the hydroxyl radical in the nighttime upper atmosphere

    Science.gov (United States)

    Campbell, Laurence; Brunger, Michael J.

    2018-02-01

    Chemical processes produce vibrationally excited hydroxyl (OH) in a layer centred at an altitude of about 87 km in the Earth's atmosphere. Observations of this layer are used to deduce temperatures in the mesosphere and to observe the passage of atmospheric gravity waves. Due to the low densities and energies at night of electrons at the relevant altitude, it is not expected that electron-impact excitation of OH would be significant. However, there are unexplained characteristics of OH densities and radiative emissions that might be explained by electron impact. These are measurements of higher than expected densities of OH above 90 km and of emissions at higher energies that cannot be explained by the chemical production processes. This study simulates the role of electron impact in these processes, using theoretical cross sections for electron-impact excitation of OH. The simulations show that electron impact, even in a substantial aurora, cannot fully explain these phenomena. However, in the process of this investigation, apparent inconsistencies in the theoretical cross sections and reaction rates were found, indicating that measurements of electron-impact excitation of OH are needed to resolve these problems and scale the theoretical predictions to allow more accurate simulations.

  4. Parametric excitation of electromagnetic waves by electron Bernstein waves

    International Nuclear Information System (INIS)

    Kuo, S.P.

    1992-01-01

    A parametric instability involving the decay of a standing electron Bernstein pump into electromagnetic sidebands and lower-hybrid decay waves is studied. A general dispersion relation is derived and analyzed. Threshold fields and growth rates are obtained for the two cases that the electron Bernstein pump is introduced near the X-mode cutoff layer or introduced in the region between the upper-hybrid resonance layer and the O-mode cutoff layer. Applications of these results to the recent observation [P. Stubbe and H. Kopka, Phys. Rev. Lett. 65, 183 (1990)] of stimulated electromagnetic emission (SEE) with a broad symmetrical structure (BSS) in the ionospheric modifications by powerful high-frequency (HF) wave are discussed

  5. Production of electronically excited NO via DEA to NO2

    Science.gov (United States)

    Gope, Krishnendu; Tadsare, Vishvesh; Prabhudesai, Vaibhav S.; Krishnakumar, E.

    2017-12-01

    Dissociative electron attachment (DEA) to NO2 in the 7-11 eV range is studied using velocity slice imaging technique. Two distinct channels are observed in the DEA corresponding to O- + NO(A 2Σ+) and O- + NO(C 2Π and/or D 2Σ+). While NO(A 2Σ+) is found to be formed only in very high vibrational levels, NO(C 2Π and/or D 2Σ+) is found to be formed with vibrational distribution starting from v = 0. From the angular distribution of the O- ions leading to the NO(C 2Π and/or D 2Σ+) channel, we obtain the symmetry of the negative ion resonance to be dominantly B1 with small contribution from B2. Contribution to the Topical Issue: "Low Energy Positron and Electron Interactions", edited by James Sullivan, Ron White, Michael Bromley, Ilya Fabrikant, and David Cassidy.

  6. Method and apparatus for secondary laser pumping by electron beam excitation

    Science.gov (United States)

    George, E. Victor; Krupke, William F.; Murray, John R.; Powell, Howard T.; Swingle, James C.; Turner, Jr., Charles E.; Rhodes, Charles K.

    1978-01-01

    An electron beam of energy typically 100 keV excites a fluorescer gas which emits ultraviolet radiation. This radiation excites and drives an adjacent laser gas by optical pumping or photolytic dissociation to produce high efficiency pulses. The invention described herein was made in the course of, or under, United States Energy Research and Development Administration Contract No. W-7405-Eng-48 with the University of California.

  7. Electron impact excitation of Fe2+. Pt. 1

    International Nuclear Information System (INIS)

    Berrington, K.A.; Eissner, W.; Burke, P.G.

    1991-01-01

    A Breit-Pauli R-matrix calculation for the electron impact collision strengths of Fe 2+ is reported involving transitions among the lowest 17 levels corresponding to the 3d 6 5 D, 3 H, 3 P, 3 F and 3 G terms. Resonance structures are elucidated for the first time. The calculated collision strengths at impact energies above the resonance region show some disagreements with those from an earlier five-term R-matrix calculation. (author)

  8. Electronic and vibrational excitations in layered high Tc superconductors

    International Nuclear Information System (INIS)

    Agarwal, B.K.; Agarwal, S.; Yadav, P.S.; Kumar, S.; Negi, J.S.; Varshney, Namrata

    1991-01-01

    In the series of the layered high T c superconductors(A)sub(1,2)B 2 Casub(n-1)Cu n Osub(2n+3,4) (A=Tl or Bi; B=Ba or Sr), with n=number of consecutive Cu-O layers, the electron energy states of some of the Tl-based systems have been investigated. The electron and phonon dispersion curves have been obtained. The electronic states near the Fermi level are dominated by the hybridized Cu(d) and the O(p) orbitals. The dispersion curves are highly two-dimensional with very small dispersion along c-axis. The number of band is enhanced with increase in the number of the consecutive Cu-O planes (n). The present results agree with those obtained earlier for other superconducting phases. The phonons are overall dominated by the vibrations of the light mass oxygen atom modes both lying in or outside the Cu-O planes. The low-frequency phonons involve the motions of the heavier Tl, Ba atoms etc. (author). 6 refs., 4 figs., 1 tab

  9. Tailoring Laser-Generated Plasmas for Efficient Nuclear Excitation by Electron Capture

    Science.gov (United States)

    Wu, Yuanbin; Gunst, Jonas; Keitel, Christoph H.; Pálffy, Adriana

    2018-02-01

    The optimal parameters for nuclear excitation by electron capture in plasma environments generated by the interaction of ultrastrong optical lasers with solid matter are investigated theoretically. As a case study we consider a 4.85 keV nuclear transition starting from the long-lived Mom93 isomer that can lead to the release of the stored 2.4 MeV excitation energy. We find that due to the complex plasma dynamics, the nuclear excitation rate and the actual number of excited nuclei do not reach their maximum at the same laser parameters. The nuclear excitation achievable with a high-power optical laser is up to twelve and up to six orders of magnitude larger than the values predicted for direct resonant and secondary plasma-mediated excitation at the x-ray free electron laser, respectively. Our results show that the experimental observation of the nuclear excitation of Mom93 and the subsequent release of stored energy should be possible at laser facilities available today.

  10. Excitation of lower hybrid waves by electron beams in finite geometry plasmas

    International Nuclear Information System (INIS)

    Shoucri, M.m.; Gagne, R.R.J.

    1978-01-01

    The quasi-static lower hybrid eigenmodes of a plasma column in a cylindrical waveguide are determined, and their linear excitation by a small density electron beam is discussed for the cases of a hot electron beam as well as for a cold electron beam. It is shown that under certain conditions, finite geometry effects introduce important quantitative and qualitative differences with respect to the results obtained in an infinite geometry. (author)

  11. Metastable Molecules in the Ground and in Excited States, Theory Development, Implementation and Application

    National Research Council Canada - National Science Library

    Bartlett, Rodney J

    2006-01-01

    ... fingerprints for identification. We also make applications of interesting clusters, atmospheric systems, potential interstellar molecules, and to gas phase molecular reactions of the sort that can occur in flames.

  12. Near-threshold electron impact excitation of argon atoms

    International Nuclear Information System (INIS)

    Ojha, P.C.; Burke, P.G.; Science and Engineering Research Council, Daresbury; Taylor, K.T.

    1982-01-01

    Theoretical cross sections are reported for the elastic and inelastic scattering of low-energy electrons (10.8-13.4eV) from the ground state of argon atoms. The calculations are carried out in the LS coupling scheme and include nine target states in the expansion of the total wavefunction. The energies and shapes of the resonances are found to agree well with the experiments of Brunt et al (J. Phys. B.; 9:2195 (1976), 10:1289 and 3781 (1977)) in most cases and their grandparent model is also confirmed although some of the present resonant assignments are different. (author)

  13. Investigations of the potential functions of weakly bound diatomic molecules and laser-assisted excitive Penning ionization

    International Nuclear Information System (INIS)

    Goble, J.H. Jr.

    1982-05-01

    Three variations on the Dunham series expansion function of the potential of a diatomic molecule are compared. The differences among these expansions lie in the choice of the expansion variable, lambda. The functional form of these variables are lambda/sub s/ = l-r/sub e//r for the Simon-Parr-Finlan version, lambda/sub T/ - 1-(r/sub e//r)/sup p/ for that of Thakkar, and lambda/sub H/ = 1-exp(-rho(r/r/sub e/-1) for that of Huffaker. A wide selection of molecular systems are examined. It is found that, for potentials in excess of thirty kcal/mole, the Huffaker expansion provides the best description of the three, extrapolating at large internuclear separation to a value within 10% of the true dissociation energy. For potentials that result from the interaction of excited states, all series expansions show poor behavior away from the equilibrium internuclear separation of the molecule. The series representation of the potentials of weakly bound molecules are examined in more detail. The ground states of BeAr + , HeNe + , NaAr, and Ar 2 and the excited states of HeNe+, NaNe, and NaAr are best described by the Thakkar expansion. Finally, the observation of laser-assisted excitive Penning ionization in a flowing afterglow is reported. The reaction Ar( 3 P 2 ) + Ca + h nu → Ar + Ca + (5p 2 P/sub J/) + e - occurs when the photon energy, h nu, is approximately equal to the energy difference between the metastable argon and one of the fine structure levels of the ion's doublet. By monitoring the cascade fluorescence of the above reaction and comparing it to the flourescence from the field-free process Ar( 3 P 2 ) + Ca → Ar + Ca + (4p 2 P/sub J/) + e - a surprisingly large cross section of 6.7 x 10 3 A 2 is estimated

  14. An area selective and anisotropic etching of Si by synchrotron radiation excitation; Effects of introducing O[sub 2] molecules

    Energy Technology Data Exchange (ETDEWEB)

    Goto, Takashi; Kitamura, Osamu; Terakado, Shingo; Suzuki, Shigeo (Sanyo Electric Co., Ltd., Tsukuba, Ibaraki (Japan). Tsukuba Research Center); Tanaka, Kenichiro

    1992-12-01

    Single crystalline silicon was photochemically etched by synchrotron radiation (SR) in the presence of reactive species produced by microwave discharge. The etching gases were a mixture of SF[sub 6] and Ar. We attempted to introduce O[sub 2] gas in order to increase the area selectivity by protecting the nonirradiated area. It was found that the introduction of O[sub 2] molecules was very effective in depressing the etching of a nonirradiated area resulting in high area selectivity. Also an anisotropic feature of c-Si was obtained by addition of O[sub 2] molecules and submicron patterning was successfully performed using a stencil mask. The effect of O[sub 2] molecules was investigated by the measurement of the spectra of total electron yield and Auger electrons. It seems that the formation of an oxide layer on c-Si surface played an important role in the area-selective etching. (author).

  15. Production of H,D(2s, 2p) by electron impact (0 - 2000 eV) on simple hydrogen containing molecules, ch. 2, A2

    International Nuclear Information System (INIS)

    Moehlman, G.R.; Heer, F.J. de

    1977-01-01

    Absolute emission cross sections of Ly-α (H,D(2p → 1s)) radiation have been determined for 0 - 2000 eV electrons incident on H 2 , HD, HCl, H 2 O, NH 3 and CH 4 . By means of the application of electric quenching, the excitation cross sections of H,D(2s) could be obtained from the increase of the resulting Ly-α radiation for these molecules. Only in the case of electrons on H 2 , D 2 and HD was excitation of H,D(2s) found

  16. Calculation of electron scattering on excited states of sodium

    International Nuclear Information System (INIS)

    Bray, I.; Fursa, D. V.; McCarthy, I.E.

    1993-11-01

    The results of electron-sodium scattering for the 3D → 3P transition at the projectile energy of 5 eV calculated using the Convergent Close Coupling method are presented. These include spin-resolved and spin-averaged alignment, orientation, and coherence parameters, as well as differential cross section and spin asymmetry. This calculation simultaneously produces results for the transitions 3P→3P at 6.52 eV and 3S → 3P at 8.62 eV. The three transitions are used to study the nature of the convergence in the close-coupling expansion. The results were found to be in good agreement with the existent experimental data. 15 refs., 9 figs

  17. Electron beam excitation assisted optical microscope with ultra-high resolution.

    Science.gov (United States)

    Inami, Wataru; Nakajima, Kentaro; Miyakawa, Atsuo; Kawata, Yoshimasa

    2010-06-07

    We propose electron beam excitation assisted optical microscope, and demonstrated its resolution higher than 50 nm. In the microscope, a light source in a few nanometers size is excited by focused electron beam in a luminescent film. The microscope makes it possible to observe dynamic behavior of living biological specimens in various surroundings, such as air or liquids. Scan speed of the nanometric light source is faster than that in conventional near-field scanning optical microscopes. The microscope enables to observe optical constants such as absorption, refractive index, polarization, and their dynamic behavior on a nanometric scale. The microscope opens new microscopy applications in nano-technology and nano-science.

  18. Studies of isotopic effects in the excited electronic states of molecular systems

    International Nuclear Information System (INIS)

    1982-01-01

    Rare gas halogen (RGH) lasers serve as convenient tools for a range of photophysical processes which exhibit isotope effects. This document summarizes progress in the production of molecular systems in their electronic excited states with the aid of RGH lasers, and the various isotopic effects one can study under these conditions. We conclude that the basic physical mechanisms involved in the isotopically sensitive characteristics of excited molecular electronic states are sufficiently selective to be useful in both the detection and separation of many atomic materials

  19. Electron-impact excitation out of the metastable levels of Krypton

    International Nuclear Information System (INIS)

    Jung, R.O.; Stone, Tom E.; Boffard, John B.; Anderson, L.W.; Lin, Chun C.

    2005-01-01

    We have measured the electron-impact excitation cross sections out of the two metastable levels of Kr into the ten levels of the 4p 5 5p configuration. For a common 4p 5 5p final level, the peak excitation cross sections out of the two individual 4p 5 5s metastable levels are found to differ by 1 to 2 orders of magnitude. This is explained by the special features of the electronic structure of the two configurations involved. The peak cross sections are 10 to 1600 times larger than the corresponding peak cross sections out of the ground state

  20. Fluorescence excitation involving multiple electron transition states of N{sub 2} and CO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Wu, C.Y.R.; Chen, F.Z.; Hung, T.; Judge, D.L. [Univ. of Southern California, Los Angeles, CA (United States)

    1997-04-01

    The electronic states and electronic structures of N{sub 2} and CO{sub 2} in the 8-50 eV energy region have been studied extensively both experimentally and theoretically. In the energy region higher than 25 eV there exists many electronic states including multiple electron transition (MET) states which are responsible for producing most of the dissociative photoionization products. The electronic states at energies higher than 50 eV have been mainly determined by Auger spectroscopy, double charge transfer, photofragment spectroscopy and ion-ion coincidence spectroscopy. The absorption and ionization spectra of these molecules at energies higher than 50 eV mainly show a monotonic decrease in cross section values and exhibit structureless features. The decay channels of MET and Rydberg (or superexcited) states include autoionization, ionization, dissociative ionization, predissociation, and dissociation while those of single ion and multiple ion states may involve predissociation. and dissociation processes. The study of fluorescence specifically probes electronically excited species resulting from the above-mentioned decay channels and provides information for understanding the competition among these channels.

  1. Rotational excitation of linear triatomic molecules: Ar, Kr + N2O, CO2

    International Nuclear Information System (INIS)

    Farrar, J.M.; Parson, J.M.; Lee, Y.T.

    1974-01-01

    Rotational excitation of N 2 O and CO 2 in collisions with Ar and Kr has been studied by crossing two supersonic molecular beams and detecting scattered products with a mass spectrometer. Measurement of the time of flight spectrum of the products as a function of laboratory scattering angle theta indicates that the inelasticity is concentrated in the forward direction in the center of mass system. Difference between CO 2 and N 2 O are discussed briefly

  2. The formation of electronically excited fragments by the electron impact of furan and related five-membered heterocycles

    International Nuclear Information System (INIS)

    Tokue, Ikuo; Ikarashi, Masami; Takizawa, Sadachika; Ito, Yoshio

    1983-01-01

    In the wavelength region of 200-600 nm, photoemissions from electronically excited H, CH, C 2 , and CS (only from thiophene and tetrahydrothiophene) were observed when furan, tetrahydrofuran, thiophene, and tetrahydrothiophene were excited by electron impact (0-70 eV). Hydrogen atoms (n = 4) and CH(A 2 Δ) radicals were produced from these five-membered heterocycles via single collision excitations, while CS(A 1 PI) radicals from thiophene and tetrahydrothiophene were partly formed in secondary processes. The appearance potentials for the hydrogen Balmer β and the CH(A 2 Δ-X 2 PI) bands from these five-membered heterocycles are determined, and the dissociation processes forming H(n = 4) and CH(A) are discussed. (author)

  3. Initial mechanisms for the decomposition of electronically excited energetic materials: 1,5′-BT, 5,5′-BT, and AzTT

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Bing; Yu, Zijun; Bernstein, Elliot R., E-mail: erb@lamar.Colostate.edu [Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872 (United States)

    2015-03-28

    Decomposition of nitrogen-rich energetic materials 1,5′-BT, 5,5′-BT, and AzTT (1,5′-Bistetrazole, 5,5′-Bistetrazole, and 5-(5-azido-(1 or 4)H-1,2,4-triazol-3-yl)tetrazole, respectively), following electronic state excitation, is investigated both experimentally and theoretically. The N{sub 2} molecule is observed as an initial decomposition product from the three materials, subsequent to UV excitation, with a cold rotational temperature (<30 K). Initial decomposition mechanisms for these three electronically excited materials are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) level illustrate that conical intersections play an essential role in the decomposition mechanism. Electronically excited S{sub 1} molecules can non-adiabatically relax to their ground electronic states through (S{sub 1}/S{sub 0}){sub CI} conical intersections. 1,5′-BT and 5,5′-BT materials have several (S{sub 1}/S{sub 0}){sub CI} conical intersections between S{sub 1} and S{sub 0} states, related to different tetrazole ring opening positions, all of which lead to N{sub 2} product formation. The N{sub 2} product for AzTT is formed primarily by N–N bond rupture of the –N{sub 3} group. The observed rotational energy distributions for the N{sub 2} products are consistent with the final structures of the respective transition states for each molecule on its S{sub 0} potential energy surface. The theoretically derived vibrational temperature of the N{sub 2} product is high, which is similar to that found for energetic salts and molecules studied previously.

  4. A screening-corrected additivity rule for the calculation of electron scattering from macro-molecules

    International Nuclear Information System (INIS)

    Blanco, F; Garcia, G

    2009-01-01

    A simplified form of the well-known screening-corrected additivity rule procedure for the calculation of electron-molecule cross sections is proposed for the treatment of some very large macro-molecules. While the comparison of the standard and simplified treatments for a DNA dodecamer reveals very similar results, the new treatment presents some important advantages for large molecules.

  5. Probing the local environment of a single OPE3 molecule using inelastic tunneling electron spectroscopy

    NARCIS (Netherlands)

    Frisenda, R.; Perrin, M.L.; Van der Zant, H.S.J.

    2015-01-01

    We study single-molecule oligo(phenylene ethynylene)dithiol junctions by means of inelastic electron tunneling spectroscopy (IETS). The molecule is contacted with gold nano-electrodes formed with the mechanically controllable break junction technique. We record the IETS spectrum of the molecule from

  6. Electronic excitations and metallization of dense solid hydrogen.

    Science.gov (United States)

    Cohen, R E; Naumov, Ivan I; Hemley, Russell J

    2013-08-20

    Theoretical calculations and an assessment of recent experimental results for dense solid hydrogen lead to a unique scenario for the metallization of hydrogen under pressure. The existence of layered structures based on graphene sheets gives rise to an electronic structure related to unique features found in graphene that are well studied in the carbon phase. The honeycombed layered structure for hydrogen at high density, first predicted in molecular calculations, produces a complex optical response. The metallization of hydrogen is very different from that originally proposed via a phase transition to a close-packed monoatomic structure, and different from simple metallization recently used to interpret recent experimental data. These different mechanisms for metallization have very different experimental signatures. We show that the shift of the main visible absorption edge does not constrain the point of band gap closure, in contrast with recent claims. This conclusion is confirmed by measured optical spectra, including spectra obtained to low photon energies in the infrared region for phases III and IV of hydrogen.

  7. Python framework for kinetic modeling of electronically excited reaction pathways

    Science.gov (United States)

    Verboncoeur, John; Parsey, Guy; Guclu, Yaman; Christlieb, Andrew

    2012-10-01

    The use of plasma energy to enhance and control the chemical reactions during combustion, a technology referred to as ``plasma assisted combustion'' (PAC), can result in a variety of beneficial effects: e.g. stable lean operation, pollution reduction, and wider range of p-T operating conditions. While experimental evidence abounds, theoretical understanding of PAC is at best incomplete, and numerical tools still lack in reliable predictive capabilities. In the context of a joint experimental-numerical effort at Michigan State University, we present here an open-source modular Python framework dedicated to the dynamic optimization of non-equilibrium PAC systems. Multiple sources of experimental reaction data, e.g. reaction rates, cross-sections and oscillator strengths, are used in order to quantify the effect of data uncertainty and limiting assumptions. A collisional-radiative model (CRM) is implemented to organize reactions by importance and as a potential means of measuring a non-Maxwellian electron energy distribution function (EEDF), when coupled to optical emission spectroscopy data. Finally, we explore scaling laws in PAC parameter space using a kinetic global model (KGM) accelerated with CRM optimized reaction sequences and sparse stiff integrators.

  8. Impact of Electron Collision Mixing on the delay times of an electron beam excited Atomic Xe laser

    NARCIS (Netherlands)

    Peters, P.J.M.; Lan, Y.F.; Lan, Yun Fu; Ohwa, Mieko; Kushner, Mark J.

    1990-01-01

    The atomic xenon (5d¿6p) infrared laser has been experimentally and theoretically investigated using a short-pulse (30-ns), high-power (1-10-MW/cm3) coaxial electron beam excitation source. In most cases, laser oscillation is not observed during the e-beam current pulse. Laser pulses of hundreds of

  9. Nonequilibrium Green function theory for excitation and transport in atoms and molecules

    NARCIS (Netherlands)

    Dahlen, Nils Erik; Stan, Adrian; Bonitz, M; Filinov, A

    2006-01-01

    In this work we discuss the application of nonequilibrium Green functions theory to atomic and molecular systems with the aim to study charge and energy transport in these systems. We apply the Kadanoff-Baym equations to atoms and diatomic molecules initially in the ground state. The results

  10. Inversion of the total cross sections for electron-molecule and electron-atom scattering

    International Nuclear Information System (INIS)

    Lun, D.R.; Amos, K.; Allen, L.J.

    1994-01-01

    Inverse scattering theory has been applied to construct the interaction potentials from total cross sections as a function of energy for electrons scattered off of atoms and molecules. The underlying potentials are assumed to be real and energy independent and are evaluated using the Eikonal approximation and with real phase shifts determined from the total cross sections. The inversion potentials have been determined using either a high energy limit approximation or by using a fixed energy inversion method at select energies. These procedures have been used to analyse e - - CH 4 , e - - SiH 4 , e - -Kr and e - -Xe scattering data in particular. 14 refs., 1 tabs., 3 figs

  11. Electron capture in ion-molecule collisions at intermediate energy

    International Nuclear Information System (INIS)

    Kumura, M.

    1986-01-01

    Recent progress of theoretical charge transfer study in ion-molecule collisions at the intermediate energy is reviewed. Concept of close and distant collisions obtained from extensive ion-atom collision studies is identified so that it can be utilized to model two distinct collision processes. For a close collision, explicit representation of the whole collision complex is necessary to describe collision dynamics correctly, while a model potential approach for molecule is appropriate for a distant collision. It is shown that these two distinct models are indeed capable of reproducing experimental charge transfer cross sections. Some remarks for further theoretical study of ion-molecule collisions are also given. 21 refs., 8 figs

  12. Electron transfer dynamics of bistable single-molecule junctions

    DEFF Research Database (Denmark)

    Danilov, A.V; Kubatkin, S.; Kafanov, S. G.

    2006-01-01

    We present transport measurements of single-molecule junctions bridged by a molecule with three benzene rings connected by two double bonds and with thiol end-groups that allow chemical binding to gold electrodes. The I-V curves show switching behavior between two distinct states. By statistical ...... analysis of the switching events, we show that a 300 meV mode mediates the transition between the two states. We propose that breaking and reformation of a S-H bond in the contact zone between molecule and electrode explains the observed bistability....

  13. Probing single-molecule electron-hole transfer dynamics at a molecule-NiO semiconductor nanocrystalline interface.

    Science.gov (United States)

    Dhital, Bharat; Rao, Vishal Govind; Lu, H Peter

    2017-07-14

    Interfacial charge transfer dynamics in dye-sensitized NiO nanoparticles are being investigated for photocathodes in p-type dye-sensitized solar cells. In the photoreaction, after fast electron transfer from NiO to a molecule, the recombination of the hole in the nanoparticles with the electron in a reduced molecule plays an important role in the charge separation process and solar energy harvesting. Nevertheless, knowledge of the interfacial charge recombination (CR) rate and its mechanism is still limited due to the complex photoinduced electron and hole dynamics and lack of characterization of the inhomogeneity of the dynamics. Here, we report our work on probing interfacial charge recombination dynamics in Zn(ii)-5,10,15,20-tetra(3-carboxyphenyl)porphyrin (m-ZnTCPP) dye-sensitized NiO nanoparticles by correlating single-molecule fluorescence blinking dynamics with charge transfer dynamics using single-molecule photon-stamping spectroscopy. The correlated analyses of single-molecule fluorescence intensity, lifetime, and blinking reveal the intrinsic distribution and temporal fluctuation of interfacial charge transfer reactivity, which are closely related to site-specific molecular interactions and dynamics.

  14. Theoretical studies of atomic and quasiatomic excitations by electron and ion impact

    International Nuclear Information System (INIS)

    Kam, K.F.

    1999-09-01

    Electron emission from ion induced excitations of Ca, Sc, Ti and V metal surfaces and from electron impact on transition metal oxides CoO and TiO 2 has been studied in this thesis. Both the autoionising emission from sputtered atoms and the 3p→3d and 3s→3d excitations in the oxides reveal strong atomic features. The work has involved explaining these spectra in an atomic approach, via the use of atomic structure calculations, cross section studies and empirical/semi-empirical analyses. The other aspect of this work involves extension of current theories of electron-atom scattering in the high electron energy impact regime. Overall it is shown that much can be learned about some solid-state spectra by relating them to atomic phenomena. (author)

  15. Second-order Born approximation for the ionization of molecules by electron and positron impact

    Energy Technology Data Exchange (ETDEWEB)

    Dal Cappello, C. [Universite Paul Verlaine-Metz, Laboratoire de Physique Moleculaire et des Collisions, Institut Jean Barriol (FR2843), 1 Boulevard Arago, F-57078 Metz Cedex 3 (France); Rezkallah, Z.; Houamer, S. [Laboratoire de Physique Quantique et Systemes Dynamiques, Departement de Physique, Faculte des Sciences Universite Ferhat Abbas, Setif 19000 (Algeria); Charpentier, I. [Universite Paul Verlaine-Metz, Laboratoire de Physique et Mecanique des Materiaux UMR 7554, Ile du Saulcy, F-57045 Metz Cedex 1 (France); Hervieux, P. A. [Institut de Physique et Chimie des Materiaux de Strasbourg, 23 Rue du Loess, BP 43, F-67034 Strasbourg Cedex 2 (France); Ruiz-Lopez, M. F. [Nancy-University, Equipe de Chimie et Biochimie Theoriques, UMR CNRS-UHP 7565, BP 239, F-54506 Vandoeuvre-les-Nancy (France); Dey, R. [Max-Planck Institut fuer Plasmaphysik, Boltzmannstr. 2, D-85748 Garching (Germany); Roy, A. C. [School of Mathematical Sciences, Ramakrishna Mission Vivekananda University, Belur Math 711202, West Bengal (India)

    2011-09-15

    Second-order Born approximation is applied to study the ionization of molecules. The initial and final states are described by single-center wave functions. For the initial state a Gaussian wave function is used while for the ejected electron it is a distorted wave. Results of the present model are compared with recent (e,2e) experiments on the water molecule. Preliminary results are also presented for the ionization of the thymine molecule by electrons and positrons.

  16. Nonlinear and Nonsymmetric Single-Molecule Electronic Properties Towards Molecular Information Processing.

    Science.gov (United States)

    Tamaki, Takashi; Ogawa, Takuji

    2017-09-05

    This review highlights molecular design for nonlinear and nonsymmetric single-molecule electronic properties such as rectification, negative differential resistance, and switching, which are important components of future single-molecule information processing devices. Perspectives on integrated "molecular circuits" are also provided. Nonlinear and nonsymmetric single-molecule electronics can be designed by utilizing (1) asymmetric molecular cores, (2) asymmetric anchoring groups, (3) an asymmetric junction environment, and (4) asymmetric electrode materials. This review mainly focuses on the design of molecular cores.

  17. Low-energy electronic excitations and band-gap renormalization in CuO

    Science.gov (United States)

    Rödl, Claudia; Ruotsalainen, Kari O.; Sottile, Francesco; Honkanen, Ari-Pekka; Ablett, James M.; Rueff, Jean-Pascal; Sirotti, Fausto; Verbeni, Roberto; Al-Zein, Ali; Reining, Lucia; Huotari, Simo

    2017-05-01

    Combining nonresonant inelastic x-ray scattering experiments with state-of-the-art ab initio many-body calculations, we investigate the electronic screening mechanisms in strongly correlated CuO in a large range of energy and momentum transfers. The excellent agreement between theory and experiment, including the low-energy charge excitations, allows us to use the calculated dynamical screening as a safe building block for many-body perturbation theory and to elucidate the crucial role played by d -d excitations in renormalizing the band gap of CuO. In this way we can dissect the contributions of different excitations to the electronic self-energy which is illuminating concerning both the general theory and this prototypical material.

  18. Isomer depletion as experimental evidence of nuclear excitation by electron capture

    Science.gov (United States)

    Chiara, C. J.; Carroll, J. J.; Carpenter, M. P.; Greene, J. P.; Hartley, D. J.; Janssens, R. V. F.; Lane, G. J.; Marsh, J. C.; Matters, D. A.; Polasik, M.; Rzadkiewicz, J.; Seweryniak, D.; Zhu, S.; Bottoni, S.; Hayes, A. B.; Karamian, S. A.

    2018-02-01

    The atomic nucleus and its electrons are often thought of as independent systems that are held together in the atom by their mutual attraction. Their interaction, however, leads to other important effects, such as providing an additional decay mode for excited nuclear states, whereby the nucleus releases energy by ejecting an atomic electron instead of by emitting a γ-ray. This ‘internal conversion’ has been known for about a hundred years and can be used to study nuclei and their interaction with their electrons. In the inverse process—nuclear excitation by electron capture (NEEC)—a free electron is captured into an atomic vacancy and can excite the nucleus to a higher-energy state, provided that the kinetic energy of the free electron plus the magnitude of its binding energy once captured matches the nuclear energy difference between the two states. NEEC was predicted in 1976 and has not hitherto been observed. Here we report evidence of NEEC in molybdenum-93 and determine the probability and cross-section for the process in a beam-based experimental scenario. Our results provide a standard for the assessment of theoretical models relevant to NEEC, which predict cross-sections that span many orders of magnitude. The greatest practical effect of the NEEC process may be on the survival of nuclei in stellar environments, in which it could excite isomers (that is, long-lived nuclear states) to shorter-lived states. Such excitations may reduce the abundance of the isotope after its production. This is an example of ‘isomer depletion’, which has been investigated previously through other reactions, but is used here to obtain evidence for NEEC.

  19. The Distribution, Excitation, and Formation of Cometary Molecules: Methanol, Methyl Cyanide, and Ethylene Glycol

    Science.gov (United States)

    Remijan, Anthony J.; Milam, Stefanie N.; Womack, Maria; Apponi, A. J.; Ziurys, L. M.; Wyckoff, Susan; A'Hearn, M. F.; de Pater, Imke; Forster, J. R.; Friedel, D. N.; Palmer, Patrick; Snyder, L. E.; Veal, J. M.; Woodney, L. M.; Wright, M. C. H.

    2008-12-01

    We present an interferometric and single-dish study of small organic species toward Comets C/1995 O1 (Hale-Bopp) and C/2002 T7 (LINEAR) using the BIMA interferometer at 3 mm and the ARO 12 m telescope at 2 mm. For Comet Hale-Bopp, both the single-dish and interferometer observations of CH3OH indicate an excitation temperature of 105 +/- 5 K and an average production rate ratio Q(CH3OH)/Q(H2O) ~ 1.3% at ~1 AU. In addition, the aperture synthesis observations of CH3OH suggest a distribution well described by a spherical outflow and no evidence of significant extended emission. Single-dish observations of CH3CN in Comet Hale-Bopp indicate an excitation temperature of 200 +/- 10 K and a production rate ratio of Q(CH3CN)/Q(H2O) ~ 0.017% at ~1 AU. The nondetection of a previously claimed transition of cometary (CH2OH)2 toward Comet Hale-Bopp with the 12 m telescope indicates a compact distribution of emission, D < 9'' (<8500 km). For the single-dish observations of Comet T7 LINEAR, we find an excitation temperature of CH3OH of 35 +/- 5 K and a CH3OH production rate ratio of Q(CH3OH)/Q(H2O) ~ 1.5% at ~0.3 AU. Our data support current chemical models that CH3OH, CH3CN, and (CH2OH)2 are parent nuclear species distributed into the coma via direct sublimation off cometary ices from the nucleus with no evidence of significant production in the outer coma.

  20. Photon emission induced by impact of electrons on molecules

    International Nuclear Information System (INIS)

    Sprang, H.A. van.

    1980-01-01

    The author discusses both the history and the present state of emission spectroscopy and presents several previously published papers giving experimental data on some diatomic molecules and for chloro-fluoro methanes. (G.T.H.)

  1. Electronic excitation of ground state atoms by collision with heavy gas particles

    Science.gov (United States)

    Hansen, C. Frederick

    1993-01-01

    Most of the important chemical reactions which occur in the very high temperature air produced around space vehicles as they enter the atmosphere were investigated both experimentally and theoretically, to some extent at least. One remaining reaction about which little is known, and which could be quite important at the extremely high temperatures that will be produced by the class of space vehicles now contemplated - such as the AOTV - is the excitation of bound electron states due to collisions between heavy gas particles. Rates of electronic excitation due to free electron collisions are known to be very rapid, but because these collisions quickly equilibrate the free and bound electron energy, the approach to full equilibrium with the heavy particle kinetic energy will depend primarily on the much slower process of bound electron excitation in heavy particle collisions and the subsequent rapid transfer to free electron energy. This may be the dominant mechanism leading to full equilibrium in the gas once the dissociation process has depleted the molecular states so the transfer between molecular vibrational energy and free electron energy is no longer available as a channel for equilibration of free electron and heavy particle kinetic energies. Two mechanisms seem probable in electronic excitation by heavy particle impact. One of these is the collision excitation and deexcitation of higher electronic states which are Rydberg like. A report, entitled 'Semi-Classical Theory of Electronic Excitation Rates', was submitted previously. This presented analytic expressions for the transition probabilities, assuming that the interaction potential is an exponential repulsion with a perturbation ripple due to the dipole-induced dipole effect in the case of neutral-neutral collisions, and to the ion-dipole interaction in the case of ion-neutral collisions. However the above may be, there is little doubt that excitation of ground state species by collision occurs at the

  2. Electron-impact coherence parameters for 41 P 1 excitation of zinc

    Science.gov (United States)

    Piwiński, Mariusz; Kłosowski, Łukasz; Chwirot, Stanisław; Fursa, Dmitry V.; Bray, Igor; Das, Tapasi; Srivastava, Rajesh

    2018-04-01

    We present electron-impact coherence parameters (EICP) for electron-impact excitation of 41 P 1 state of zinc atoms for collision energies 40 eV and 60 eV. The experimental results are presented together with convergent close-coupling and relativistic distorted-wave approximation theoretical predictions. The results are compared and discussed with EICP data for collision energies 80 eV and 100 eV.

  3. Electronic Transport in Single Molecule Junctions: Control of the Molecule-Electrode Coupling Through Intramolecular Tunneling Barriers

    DEFF Research Database (Denmark)

    Danilov, Andrey; Kubatkin, Sergey; Kafanov, Sergey

    2008-01-01

    We report on single molecule electron transport measurements of two oligophenylenevinylene (OPV3) derivatives placed in a nanogap between gold (Au) or lead (Pb) electrodes in a field effect transistor device. Both derivatives contain thiol end groups that allow chemical binding to the electrodes...... to sequential tunneling and Coulomb blockade behavior....

  4. An MRCI investigation of the electronically excited states of difluorocarbene and its monovalent ions

    Czech Academy of Sciences Publication Activity Database

    Czernek, Jiří; Živný, O.

    2008-01-01

    Roč. 106, č. 14 (2008), s. 1761-1765 ISSN 0026-8976 Grant - others:GA ČR(CZ) GA102/06/1337 Institutional research plan: CEZ:AV0Z40500505 Keywords : carbenes * excited states * ab initio Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.478, year: 2008

  5. Electron impact excitation collision strengths for neon-like Ni XIX ...

    Indian Academy of Sciences (India)

    In a recent paper [Pramana - J. Phys. 64, 129 (2005)] results have been presented for electron impact excitation collision strengths for transitions among the fine-structure levels of the 2s22p6 and 2s22p53s configurations of Ni XIX. In this paper we demonstrate through an independent calculation with the relativistic -matrix ...

  6. Evidence for resonance electron transfer in photon excited X-ray ...

    Indian Academy of Sciences (India)

    is also measured. The measured relative intensities are compared with the theoretical estimates of Aberg. Keywords. X-ray satellites; resonance electron transfer; crystal spectrometer. PACS Nos 32.30.Rj; 32.80.Hd; 78.70.En. 1. Introduction. When an atom ionized simultaneously in different shells de-excites, X-ray satellites.

  7. Evidence for resonance electron transfer in photon excited X-ray ...

    Indian Academy of Sciences (India)

    Evidence for resonance electron transfer in photon excited X-ray satellite spectra of fluorine compounds. K Ram Narayana B Seetharami Reddy S S Raju T Seshi Reddy S Lakshmi Narayana K Premachand B M Rao M V R Murti L S Mombasawala. Research Articles Volume 65 Issue 2 August 2005 pp 285-290 ...

  8. HE2+-HE COLLISIONS - ONE-ELECTRON CAPTURE AND TARGET-ION EXCITATION

    NARCIS (Netherlands)

    FOLKERTS, HO; BLIEK, FW; MENG, L; OLSON, RE; MORGENSTERN, R; VONHELLERMANN, M; SUMMERS, HP; HOEKSTRA, R

    1994-01-01

    By means of photon emission spectroscopy we have studied state selective one-electron capture and target-ion excitation in collisions of He-2+ with He. The collision energy has been varied from 1 to 75 keV amu-1 Four-body classical trajectory Monte Carlo calculations have been performed in the

  9. Electron impact excitation of the D states of Mg, Ca and Sr atoms ...

    Indian Academy of Sciences (India)

    Electron impact excitation of the states of Mg, Ca and Sr atoms: Complete experiment results. Sachin Saxena Kshamata Muktavat Rajesh Srivastava. Research Articles Volume 63 Issue 5 November 2004 pp 977-991 ... Good agreement is found on comparison and the importance of relativistic effects is also explored.

  10. Excitation of lower hybrid waves by electron beams in finite geometry plasmas

    International Nuclear Information System (INIS)

    Gagne, R.R.J.; Shoucri, M.M.

    1978-01-01

    The dispersion relations for the quasi-static lower hybrid surface waves are derived. Conditions for their existence and their linear excitation by a small density electron beam are discussed. Instabilities appearing in low-frequency surface waves are also discussed. (author)

  11. Electron impact excitation collision strengths for neon-like Ni XIX ...

    Indian Academy of Sciences (India)

    Abstract. In a recent paper [Pramana – J. Phys. 64, 129 (2005)] results have been presented for electron impact excitation collision strengths for transitions among the fine- structure levels of the 2s22p6 and 2s22p53s configurations of Ni XIX. In this paper we demonstrate through an independent calculation with the ...

  12. Dimensionality of electronic excitations in organic semiconductors: A dielectric function approach

    Science.gov (United States)

    Campoy-Quiles, Mariano; Nelson, Jenny; Bradley, Donal D. C.; Etchegoin, Pablo G.

    2007-12-01

    We present a detailed investigation on the effective dimensionality (associated with the degree of delocalization) of electronic excitations in thin organic films using the dielectric function as obtained from ellipsometry. To this end, we study first the best analytical representation of the optical dielectric function of these materials and compare different approaches found in the literature: (i) the harmonic oscillator approximation, (ii) the standard critical-point model (SCP), (iii) the model dielectric function (MDF), and (iv) the Forouhi-Bloomer model. We use these models to analyze variable angle spectroscopic ellipsometry raw data for a thin poly(9,9-dioctylfluorene) (PFO) film deposited on quartz (taken as an archetypal sample). The superiority of the SCP model for PFO films and a wide range of other spin-coated conjugated polymers (and guest-molecules in polymers) is demonstrated. Moreover, we show how the SCP model can be used to gain physical information on the microscopic structure. As an example, we show that the delocalization of excitons decreases for nonconjugated polymers, such as polymethylmethacrylate and polyimide, while the conjugation length and exciton delocalization are, respectively, enhanced in cases where a planar conformation (e.g., β phase of PFO) or a high degree of crystallinity [e.g., poly(3-hexylthiophene)] is achieved. As an additional example, we employ the SCP excitonic model to investigate the temperature dependence of the dielectric function of crystalline and glassy PFO films. We propose that the SCP excitonic model should be adopted as the standard choice to model the optical properties of polymer thin films from ellipsometry data.

  13. Nonequilibrium Green function theory for excitation and transport in atoms and molecules

    International Nuclear Information System (INIS)

    Dahlen, Nils Erik; Stan, Adrian; Leeuwen, Robert van

    2006-01-01

    In this work we discuss the application of nonequilibrium Green functions theory to atomic and molecular systems with the aim to study charge and energy transport in these systems. We apply the Kadanoff-Baym equations to atoms and diatomic molecules initially in the ground state. The results obtained for the correlated initial states are used to analyze variational energy functionals of the Green function which are shown to perform very well. We further show an application of the Kadanoff-Baym equations to a molecule exposed to an external laser field. Finally we discuss the connection between nonequilibrium Green function theory and time-dependent density-functional theory with the aim to develop better density functionals in order to treat larger systems than those attainable with the nonequilibrium Green function method

  14. Electronic structure and bonding in the RhC molecule by all-electron ab initio HF–Cl calculations and mass spectrometric measurements

    DEFF Research Database (Denmark)

    Shim, Irene; Gingerich, K. A.

    1984-01-01

    In the present study we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of the 2Sigma+ ground state as well as of 16 excited states of the RhC molecule. The calculated spectroscopic constants of the lowest lying states are in good agreement...... with the experimental data. The chemical bond in the electronic ground state is mainly due to interaction of the 4d orbitals of Rh with the 2s and 2p orbitals of C. The bond is a triple bond composed of two pi bonds and one sigma bond. The 5s electron of Rh hardly participates in the bond formation. It is located...

  15. Laser excitation of 8-eV electronic states in Th{sup +}. A first pillar of the electronic bridge toward excitation of the Th-229 nucleus

    Energy Technology Data Exchange (ETDEWEB)

    Herrera-Sancho, Oscar-Andrey

    2012-11-23

    The possibility to realize a nuclear clock based on the optical magnetic dipole transition from the ground state to the low-energy isomeric state in the {sup 229}Th nucleus has motivated experiments and proposals toward highly accurate clocks with trapped ions and highly stable optical frequency standards with Th-doped solids. These systems hold great promise to open a field of research in the borderland between atomic and nuclear physics, which will enable highly sensitive tests of postulates from fundamental physics and also will allow us to coherently excite and control nuclear states, opening a wonderful and intriguing new field in physics. A major experimental obstacle that has to be overcome before any precision spectroscopy can be performed with this system is however the insufficient knowledge on the exact transition energy. The best experimental result so far is an indirect determination from {gamma}-spectroscopy with a relative uncertainty of about 6%. To facilitate the search for the nuclear transition within a wide uncertainty range around 8 eV, we investigate two-photon excitation in the dense electronic level structure of Th{sup +}, which enables the nuclear excitation via a resonantly enhanced inverse electronic bridge process. Experiments on one- and two-photon laser excitation of buffer gas cooled {sup 232}Th{sup +} ions in a radio-frequency ion trap are reported in this thesis. The strongest resonance line at 402 nm from the (6d{sup 2}7s)J=3/2 ground state to the (6d7s7p)J=5/2 state is driven as the first excitation step. Using nanosecond laser pulses in the 250-nm wavelength range for the second step of a two-photon excitation, we have observed seven previously unknown levels in the unexplored region of the electronic level structure around 8 eV. This investigation shows that the Th{sup +} ion seems to be well suited for the search of the isomer transition because both, theory and experimental results, agree on the density of strong transitions

  16. Restricted second random phase approximations and Tamm-Dancoff approximations for electronic excitation energy calculations.

    Science.gov (United States)

    Peng, Degao; Yang, Yang; Zhang, Peng; Yang, Weitao

    2014-12-07

    In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N(4)). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as ⟨Ŝ(2)⟩ are also developed and tested.

  17. On the Electronic Structures and Electron Affinities of the m- Benzoquinone (BQ) Diradical and the o-, p-BQ Molecules: A Synergetic Photoelectron Spectroscopic and Theoretical Study

    International Nuclear Information System (INIS)

    Fu, Qiang; Yang, Jinlong; Wang, Xue B.

    2011-01-01

    Electron affinities (EAs) and electronic structures of benzoquinone molecules (BQs) play a vital role in a wide range of applications involving these molecules from biological photosynthesis to energy conversion processes. In this article, we report a systematic spectroscopic probe on the electronic structures and EAs of all three isomers (o-, m-, and p-BQs) employing photodetachment photoelectron spectroscopy (PES) and ab initio electronic structure calculations. PES spectra of three radical anions (BQ(lg b ullet)-) were taken with different photon energies and at low temperature in order to accurately determine the EAs and probe ground as well as the excited states of the corresponding neutral molecules. Similar spectral pattern was observed in the o- and p-BQ(lg b ullet)- spectra, each revealing a broad ground state feature and a large band gap, followed by well-resolved excited states peaks. The EAs of o- and p-BQ are determined to be 1.90, 1.85 eV, and singlet-triplet band gaps to be 1.68, and 2.32 eV, respectively. In contrast, the spectrum of m-BQ(lg b ullet)- is distinctly different from its two congeners, with no clear band gap and a much higher EA (2.89 eV). Accompanying theoretical calculations confirm experimental EAs and band gaps, and further unravel a triplet ground state for m-BQ in contrast to singlet ground states for o- and p- isomers. The diradical nature of m-BQ, consistent with its non-Kekule structure, is primarily responsible for the observed high EA and also explains its nonexistence in bulk materials.

  18. Electronic absorption spectra and geometry of organic molecules an application of molecular orbital theory

    CERN Document Server

    Suzuki, Hiroshi

    1967-01-01

    Electronic Absorption Spectra and Geometry of Organic Molecules: An Application of Molecular Orbital Theory focuses on electronic absorption spectra of organic compounds and molecules. The book begins with the discussions on molecular spectra, electronic absorption spectra of organic compounds, and practical measures of absorption intensity. The text also focuses on molecular orbital theory and group theory. Molecular state functions; fundamental postulates of quantum theory; representation of symmetry groups; and symmetry operations and symmetry groups are described. The book also dis

  19. Application of the method of continued fractions for electron scattering by linear molecules

    International Nuclear Information System (INIS)

    Lee, M.-T.; Iga, I.; Fujimoto, M.M.; Lara, O.; Brasilia Univ., DF

    1995-01-01

    The method of continued fractions (MCF) of Horacek and Sasakawa is adapted for the first time to study low-energy electron scattering by linear molecules. Particularly, we have calculated the reactance K-matrices for an electron scattered by hydrogen molecule and hydrogen molecular ion as well as by a polar LiH molecule in the static-exchange level. For all the applications studied herein. the calculated physical quantities converge rapidly, even for a strongly polar molecule such as LiH, to the correct values and in most cases the convergence is monotonic. Our study suggests that the MCF could be an efficient method for studying electron-molecule scattering and also photoionization of molecules. (Author)

  20. Rate coefficients for reactive elementary processes involving atoms and vibrationally excited molecules

    International Nuclear Information System (INIS)

    Lagana, A.

    1996-01-01

    To investigate reactions of atoms with simple molecules wa are both developing new computational approaches and applying consolidated efficient numerical procedures to the calculation of experimental observables under a wide range of operating conditions. Our work on the design of new theoretical and computational approaches to the accurate three dimensional calculation of reactive properties from first principles is based upon the use of the hyperspherical formalism. On the contrary, our work on the design of efficient parallel codes dealing with quantum reduced dimensionality techniques is based upon the use of Jacobi coordinates. The trajectory code makes use of position vectors with respect to the center of mass of the system. (author)

  1. Vibrational Excitation of Diatomic Molecular Ions in Strong Field Ionization of Diatomic Molecules

    International Nuclear Information System (INIS)

    Kjeldsen, Thomas K.; Madsen, Lars Bojer

    2005-01-01

    A model based on the strong-field and Born-Oppenheimer approximations qualitatively describes the distribution over vibrational states formed in a diatomic molecular ion following ionization of the neutral molecule by intense laser pulses. Good agreement is found with a recent experiment [X. Urbain et al., Phys. Rev. Lett. 92, 163004 (2004)]. In particular, the observed deviation from a Franck-Condon-like distribution is reproduced. Additionally, we demonstrate control of the vibrational distribution by a variation of the peak intensity or a change of frequency of the laser pulse

  2. Construction of Vibronic Diabatic Hamiltonian for Excited-State Electron and Energy Transfer Processes.

    Science.gov (United States)

    Xie, Yu; Jiang, Shengshi; Zheng, Jie; Lan, Zhenggang

    2017-12-21

    Photoinduced excited-state electron and energy transfer processes are crucial in biological photoharvesting systems and organic photovoltaic devices. We discuss the construction of a diabatic vibronic Hamiltonian for the proper treatment of these processes involving the projection approach acting on both electronic wave functions and vibrational modes. In the electronic part, the wave function projection approach is used to construct the diabatic Hamiltonian in which both local excited states and charge-transfer states are included on the same footing. For the vibrational degrees of freedom, the vibronic couplings in the diabatic Hamiltonian are obtained in the basis of the pseudonormal modes localized on each monomer site by applying delocalized-to-localized mode projection. This systematic approach allows us to construct the vibronic diabatic Hamiltonian in molecular aggregates.

  3. Defect production and annihilation in metals through electronic excitation by energetic heavy ion bombardment

    Energy Technology Data Exchange (ETDEWEB)

    Iwase, Akihiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1997-03-01

    Defect production, radiation annealing and defect recovery are studied in Ni and Cu irradiated with low-energy ({approx}1-MeV) and high-energy ({approx}100-MeV) ions. Irradiation of Ni with {approx}100-MeV ions causes an anomalous reduction, or even a complete disappearance of the stage-I recovery. This result shows that the energy transferred from excited electrons to lattice atoms through the electron-lattice interaction contributes to the annihilation of the stage-I interstitials. This effect is also observed in Ni as a large radiation annealing during 100-MeV heavy ion irradiation. On the other hand, in Cu thin foils, we find the defect production process strongly associated with electron excitation, where the defect production cross section is nearly proportional to S{sub e}{sup 2}. (author)

  4. Delta self-consistent field method to obtain potential energy surfaces of excited molecules on surfaces

    DEFF Research Database (Denmark)

    Gavnholt, Jeppe; Olsen, Thomas; Engelund, Mads

    2008-01-01

    is a density-functional method closely resembling standard density-functional theory (DFT), the only difference being that in Delta SCF one or more electrons are placed in higher lying Kohn-Sham orbitals instead of placing all electrons in the lowest possible orbitals as one does when calculating the ground......-photoemission spectroscopy measurements. This comparison shows that the modified Delta SCF method gives results in close agreement with experiment, significantly closer than the comparable methods. For N2 adsorbed on ruthenium (0001) we map out a two-dimensional part of the potential energy surfaces in the ground state...

  5. Minimum in the high-order harmonic generation spectrum from molecules: role of excited states

    DEFF Research Database (Denmark)

    Han, Yong-Chang; Madsen, Lars Bojer

    2010-01-01

    We model the process of high-order harmonic generation by solving the time-dependent Schrödinger equation for H+2 in the fixed nuclei approximation including full 3D electron motion for nonvanishing angles between the nuclear axis and the linear polarization of the driving pulse. We show that the......We model the process of high-order harmonic generation by solving the time-dependent Schrödinger equation for H+2 in the fixed nuclei approximation including full 3D electron motion for nonvanishing angles between the nuclear axis and the linear polarization of the driving pulse. We show...

  6. Investigations of the potential functions of weakly bound diatomic molecules and laser-assisted excitive Penning ionization

    Energy Technology Data Exchange (ETDEWEB)

    Goble, J.H. Jr.

    1982-05-01

    Three variations on the Dunham series expansion function of the potential of a diatomic molecule are compared. The differences among these expansions lie in the choice of the expansion variable, lambda. The functional form of these variables are lambda/sub s/ = l-r/sub e//r for the Simon-Parr-Finlan version, lambda/sub T/ - 1-(r/sub e//r)/sup p/ for that of Thakkar, and lambda/sub H/ = 1-exp(-rho(r/r/sub e/-1) for that of Huffaker. A wide selection of molecular systems are examined. It is found that, for potentials in excess of thirty kcal/mole, the Huffaker expansion provides the best description of the three, extrapolating at large internuclear separation to a value within 10% of the true dissociation energy. For potentials that result from the interaction of excited states, all series expansions show poor behavior away from the equilibrium internuclear separation of the molecule. The series representation of the potentials of weakly bound molecules are examined in more detail. The ground states of BeAr/sup +/, HeNe/sup +/, NaAr, and Ar/sub 2/ and the excited states of HeNe+, NaNe, and NaAr are best described by the Thakkar expansion. Finally, the observation of laser-assisted excitive Penning ionization in a flowing afterglow is reported. The reaction Ar(/sup 3/P/sub 2/) + Ca + h nu ..-->.. Ar + Ca/sup +/(5p /sup 2/P/sub J/) + e/sup -/ occurs when the photon energy, h nu, is approximately equal to the energy difference between the metastable argon and one of the fine structure levels of the ion's doublet. By monitoring the cascade fluorescence of the above reaction and comparing it to the flourescence from the field-free process Ar(/sup 3/P/sub 2/) + Ca ..-->.. Ar + Ca/sup +/(4p /sup 2/P/sub J/) + e/sup -/ a surprisingly large cross section of 6.7 x 10/sup 3/ A/sup 2/ is estimated.

  7. Transient Melting and Recrystallization of Semiconductor Nanocrystals Under Multiple Electron-Hole Pair Excitation.

    Science.gov (United States)

    Kirschner, Matthew S; Hannah, Daniel C; Diroll, Benjamin T; Zhang, Xiaoyi; Wagner, Michael J; Hayes, Dugan; Chang, Angela Y; Rowland, Clare E; Lethiec, Clotilde M; Schatz, George C; Chen, Lin X; Schaller, Richard D

    2017-09-13

    Ultrafast optical pump, X-ray diffraction probe experiments were performed on CdSe nanocrystal (NC) colloidal dispersions as functions of particle size, polytype, and pump fluence. Bragg peak shifts related to heating and peak amplitude reduction associated with lattice disordering are observed. For smaller NCs, melting initiates upon absorption of as few as ∼15 electron-hole pair excitations per NC on average (0.89 excitations/nm 3 for a 1.5 nm radius) with roughly the same excitation density inducing melting for all examined NCs. Diffraction intensity recovery kinetics, attributable to recrystallization, occur over hundreds of picoseconds with slower recoveries for larger particles. Zincblende and wurtzite NCs revert to initial structures following intense photoexcitation suggesting melting occurs primarily at the surface, as supported by simulations. Electronic structure calculations relate significant band gap narrowing with decreased crystallinity. These findings reflect the need to consider the physical stability of nanomaterials and related electronic impacts in high intensity excitation applications such as lasing and solid-state lighting.

  8. Electronic-excitation decay kinetics in disordered media: Independent-modes approximation

    International Nuclear Information System (INIS)

    Vugmeister, B.E.; Lax, M.

    1992-01-01

    An approach to the theory of electron energy transport between randomly situated donors, based on expanding the kinetic equations valid for fixed donor space positions into a spatial Fourier series and neglecting the interaction betwen different Fourier components, is proposed. The decay of occupancy of donor sites due to excitation migration is obtained for all time scales, for the case of dipole-dipole interaction between donors. The effect of back migration to the initial donor is included and a reasonable value for the stationary diffusion coefficient is obtained. The present approach yields an adequate dependence of diffusion coefficients on the cross-relaxation form factor in inhomogeneously broadened excitation spectra

  9. Spin excitations and the electronic specific heat of URu2Si2

    DEFF Research Database (Denmark)

    Mason, T.E.; Buyers, W.J.L.

    1991-01-01

    and conduction electrons yields m*/m(b) almost-equal-to 7.7 for T T(N) which is sufficient to account for the difference between band-structure calculations and the measured electronic specific heat. In addition, inclusion of the temperature dependence of the spin......We have calculated the mass enhancement due to the interaction of conduction electrons with spin fluctuations, using the generalized spin susceptibility determined from neutron-scattering measurements, for the heavy-fermion superconductor URu2Si2. Reasonable coupling between the spin excitations...

  10. Electron Transport in Quantum Dots and Heat Transport in Molecules

    DEFF Research Database (Denmark)

    Kirsanskas, Gediminas

    to make a device in order to get fundamentally new properties?” [1], or more concretely, when do the quantum effects become important. During the last 30 years, the innovations in fabrication and cooling techniques allowed to produce nanometer scale solid-state or single molecule-based devices...

  11. Cooling and Laser-Induced Fluorescence of Electronically-Excited He2 in a Supersonic Microcavity Plasma Jet

    Science.gov (United States)

    Su, Rui; Mironov, Andrey; Houlahan, Thomas, Jr.; Eden, J. Gary; LaboratoryOptical Physics; Engineering Team

    2016-09-01

    Laser-induced fluorescence (LIF) resulting from transitions between different electronic states of helium dimers generated within a microcavity plasma jet was studied with rotational resolution. In particular, the d3Σu+ , e3Πg and f3Σu+ states, all having electronic energies above 24 eV, are populated by a microplasma in 4 bar of helium gas and rotationally cooled through supersonic expansion. Analysis of two dimensional maps (spectrograms) of dimer emission spectra as a function of distance from the nozzle orifice indicates collisional coupling during the expansion between the lowest rotational levels of the e3Πg , f3Σu+ states and high rotational levels (around N=11) of the d3Σu+ state (all of which are in the v = 0 vibrational state). In an attempt to verify the coupling, a scanning dye laser (centered near 596 nm) pumps the b3Πg -> f3Σu+ transition of the molecule several hundred micrometers downstream of the nozzle. As a result, the emission intensities of relevant rotational lines are observed to be enhanced. This research shows the potential of utilizing microcavity plasma jets as a tool to study and manipulate the collisional dynamics of highly-excited diatomic molecules.

  12. Opto-electronic properties of charged conjugated molecules

    NARCIS (Netherlands)

    Fratiloiu, S.

    2007-01-01

    The aim of this thesis is to provide fundamental insight into the nature and opto-electronic properties of charge carriers on conjugated oligomers and polymers. Electronic structure, optical absorption properties and distribution of charge carriers along the chains of different conjugated materials

  13. Studying σ 54-dependent transcription at the single-molecule level using alternating-laser excitation (ALEX) spectroscopy

    Science.gov (United States)

    Heilemann, M.; Lymperopoulos, K.; Wigneshweraraj, S. R.; Buck, M.; Kapanidis, A. N.

    2007-07-01

    We present single-molecule fluorescence studies of σ 54-dependent gene-transcription complexes using singlemolecule fluorescence resonance energy transfer (smFRET) and alternating-laser excitation (ALEX) spectroscopy. The ability to study one biomolecule at the time allowed us to resolve and analyze sample heterogeneities and extract structural information on subpopulations and transient intermediates of transcription; such information is hidden in bulk experiments. Using site-specifically labeled σ 54 derivatives and site-specifically labeled promoter-DNA fragments, we demonstrate that we can observe single diffusing σ 54-DNA and transcription-initiation RNA polymerase-σ 54- DNA complexes, and that we can measure distances within such complexes; the identity of the complexes has been confirmed using electrophoretic-mobility-shift assays. Our studies pave the way for understanding the mechanism of abortive initiation and promoter escape in σ 54-dependent transcription.

  14. The structural, electronic and spectroscopic properties of 4FPBAPE molecule: Experimental and theoretical study

    Science.gov (United States)

    Tanış, Emine; Babur Sas, Emine; Kurban, Mustafa; Kurt, Mustafa

    2018-02-01

    The experimental and theoretical study of 4-Formyl Phenyl Boronic Acid Pinacol Ester (4FPBAPE) molecule were performed in this work. 1H, 13C NMR and UV-Vis spectra were tested in dimethyl sulfoxide (DMSO). The structural, spectroscopic properties and energies of 4FPBAPE were obtained for two potential conformers from density functional theory (DFT) with B3LYP/6-311G (d, p) and CAM-B3LYP/6-311G (d, p) basis sets. The optimal geometry of those structures was obtained according to the position of oxygen atom upon determining the scan coordinates for each conformation. The most stable conformer was found as the A2 form. The fundamental vibrations were determined based on optimized structure in terms of total energy distribution. Electronic properties such as oscillator strength, wavelength, excitation energy, HOMO, LUMO and molecular electrostatic potential and structural properties such as radial distribution functions (RDF) and probability density depending on coordination number are presented. Theoretical results of 4-FPBAPE spectra were found to be compatible with observed spectra.

  15. Multiconfiguration Pair-Density Functional Theory Is as Accurate as CASPT2 for Electronic Excitation.

    Science.gov (United States)

    Hoyer, Chad E; Ghosh, Soumen; Truhlar, Donald G; Gagliardi, Laura

    2016-02-04

    A correct description of electronically excited states is critical to the interpretation of visible-ultraviolet spectra, photochemical reactions, and excited-state charge-transfer processes in chemical systems. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory and a new kind of density functional called an on-top density functional. Here, we show that MC-PDFT with a first-generation on-top density functional performs as well as CASPT2 for an organic chemistry database including valence, Rydberg, and charge-transfer excitations. The results are very encouraging for practical applications.

  16. Inelastic electron and Raman scattering from the collective excitations in quantum wires: Zero magnetic field

    Directory of Open Access Journals (Sweden)

    Manvir S. Kushwaha

    2013-04-01

    Full Text Available The nanofabrication technology has taught us that an m-dimensional confining potential imposed upon an n-dimensional electron gas paves the way to a quasi-(n-m-dimensional electron gas, with m ⩽ n and 1 ⩽ n, m ⩽ 3. This is the road to the (semiconducting quasi-n dimensional electron gas systems we have been happily traversing on now for almost two decades. Achieving quasi-one dimensional electron gas (Q-1DEG [or quantum wire(s for more practical purposes] led us to some mixed moments in this journey: while the reduced phase space for the scattering led us believe in the route to the faster electron devices, the proximity to the 1D systems left us in the dilemma of describing it as a Fermi liquid or as a Luttinger liquid. No one had ever suspected the potential of the former, but it took quite a while for some to convince the others on the latter. A realistic Q-1DEG system at the low temperatures is best describable as a Fermi liquid rather than as a Luttinger liquid. In the language of condensed matter physics, a critical scrutiny of Q-1DEG systems has provided us with a host of exotic (electronic, optical, and transport phenomena unseen in their higher- or lower-dimensional counterparts. This has motivated us to undertake a systematic investigation of the inelastic electron scattering (IES and the inelastic light scattering (ILS from the elementary electronic excitations in quantum wires. We begin with the Kubo's correlation functions to derive the generalized dielectric function, the inverse dielectric function, and the Dyson equation for the dynamic screened potential in the framework of Bohm-Pines’ random-phase approximation. These fundamental tools then lead us to develop methodically the theory of IES and ILS for the Q-1DEG systems. As an application of the general formal results, which know no bounds regarding the subband occupancy, we compute the density of states, the Fermi energy, the full excitation spectrum [comprised of

  17. Inelastic electron and Raman scattering from the collective excitations in quantum wires: Zero magnetic field

    Science.gov (United States)

    Kushwaha, Manvir S.

    2013-04-01

    The nanofabrication technology has taught us that an m-dimensional confining potential imposed upon an n-dimensional electron gas paves the way to a quasi-(n-m)-dimensional electron gas, with m ⩽ n and 1 ⩽ n, m ⩽ 3. This is the road to the (semiconducting) quasi-n dimensional electron gas systems we have been happily traversing on now for almost two decades. Achieving quasi-one dimensional electron gas (Q-1DEG) [or quantum wire(s) for more practical purposes] led us to some mixed moments in this journey: while the reduced phase space for the scattering led us believe in the route to the faster electron devices, the proximity to the 1D systems left us in the dilemma of describing it as a Fermi liquid or as a Luttinger liquid. No one had ever suspected the potential of the former, but it took quite a while for some to convince the others on the latter. A realistic Q-1DEG system at the low temperatures is best describable as a Fermi liquid rather than as a Luttinger liquid. In the language of condensed matter physics, a critical scrutiny of Q-1DEG systems has provided us with a host of exotic (electronic, optical, and transport) phenomena unseen in their higher- or lower-dimensional counterparts. This has motivated us to undertake a systematic investigation of the inelastic electron scattering (IES) and the inelastic light scattering (ILS) from the elementary electronic excitations in quantum wires. We begin with the Kubo's correlation functions to derive the generalized dielectric function, the inverse dielectric function, and the Dyson equation for the dynamic screened potential in the framework of Bohm-Pines' random-phase approximation. These fundamental tools then lead us to develop methodically the theory of IES and ILS for the Q-1DEG systems. As an application of the general formal results, which know no bounds regarding the subband occupancy, we compute the density of states, the Fermi energy, the full excitation spectrum [comprised of intrasubband and

  18. Search for excited electrons in p pmacr collisions at s=1.96TeV

    Science.gov (United States)

    Abazov, V. M.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adams, M.; Adams, T.; Aguilo, E.; Ahn, S. H.; Ahsan, M.; Alexeev, G. D.; Alkhazov, G.; Alton, A.; Alverson, G.; Alves, G. A.; Anastasoaie, M.; Ancu, L. S.; Andeen, T.; Anderson, S.; Andrieu, B.; Anzelc, M. S.; Arnoud, Y.; Arov, M.; Arthaud, M.; Askew, A.; Åsman, B.; Assis Jesus, A. C. S.; Atramentov, O.; Autermann, C.; Avila, C.; Ay, C.; Badaud, F.; Baden, A.; Bagby, L.; Baldin, B.; Bandurin, D. V.; Banerjee, S.; Banerjee, P.; Barberis, E.; Barfuss, A.-F.; Bargassa, P.; Baringer, P.; Barreto, J.; Bartlett, J. F.; Bassler, U.; Bauer, D.; Beale, S.; Bean, A.; Begalli, M.; Begel, M.; Belanger-Champagne, C.; Bellantoni, L.; Bellavance, A.; Benitez, J. A.; Beri, S. B.; Bernardi, G.; Bernhard, R.; Bertram, I.; Besançon, M.; Beuselinck, R.; Bezzubov, V. A.; Bhat, P. C.; Bhatnagar, V.; Biscarat, C.; Blazey, G.; Blekman, F.; Blessing, S.; Bloch, D.; Bloom, K.; Boehnlein, A.; Boline, D.; Bolton, T. A.; Borissov, G.; Bose, T.; Brandt, A.; Brock, R.; Brooijmans, G.; Bross, A.; Brown, D.; Buchanan, N. J.; Buchholz, D.; Buehler, M.; Buescher, V.; Bunichev, V.; Burdin, S.; Burke, S.; Burnett, T. H.; Buszello, C. P.; Butler, J. M.; Calfayan, P.; Calvet, S.; Cammin, J.; Carvalho, W.; Casey, B. C. K.; Cason, N. M.; Castilla-Valdez, H.; Chakrabarti, S.; Chakraborty, D.; Chan, K. M.; Chan, K.; Chandra, A.; Charles, F.; Cheu, E.; Chevallier, F.; Cho, D. K.; Choi, S.; Choudhary, B.; Christofek, L.; Christoudias, T.; Cihangir, S.; Claes, D.; Coadou, Y.; Cooke, M.; Cooper, W. E.; Corcoran, M.; Couderc, F.; Cousinou, M.-C.; Crépé-Renaudin, S.; Cutts, D.; Ćwiok, M.; da Motta, H.; Das, A.; Davies, G.; de, K.; de Jong, S. J.; de La Cruz-Burelo, E.; de Oliveira Martins, C.; Degenhardt, J. D.; Déliot, F.; Demarteau, M.; Demina, R.; Denisov, D.; Denisov, S. P.; Desai, S.; Diehl, H. T.; Diesburg, M.; Dominguez, A.; Dong, H.; Dudko, L. V.; Duflot, L.; Dugad, S. R.; Duggan, D.; Duperrin, A.; Dyer, J.; Dyshkant, A.; Eads, M.; Edmunds, D.; Ellison, J.; Elvira, V. D.; Enari, Y.; Eno, S.; Ermolov, P.; Evans, H.; Evdokimov, A.; Evdokimov, V. N.; Ferapontov, A. V.; Ferbel, T.; Fiedler, F.; Filthaut, F.; Fisher, W.; Fisk, H. E.; Ford, M.; Fortner, M.; Fox, H.; Fu, S.; Fuess, S.; Gadfort, T.; Galea, C. F.; Gallas, E.; Galyaev, E.; Garcia, C.; Garcia-Bellido, A.; Gavrilov, V.; Gay, P.; Geist, W.; Gelé, D.; Gerber, C. E.; Gershtein, Y.; Gillberg, D.; Ginther, G.; Gollub, N.; Gómez, B.; Goussiou, A.; Grannis, P. D.; Greenlee, H.; Greenwood, Z. D.; Gregores, E. M.; Grenier, G.; Gris, Ph.; Grivaz, J.-F.; Grohsjean, A.; Grünendahl, S.; Grünewald, M. W.; Guo, J.; Guo, F.; Gutierrez, P.; Gutierrez, G.; Haas, A.; Hadley, N. J.; Haefner, P.; Hagopian, S.; Haley, J.; Hall, I.; Hall, R. E.; Han, L.; Hansson, P.; Harder, K.; Harel, A.; Harrington, R.; Hauptman, J. M.; Hauser, R.; Hays, J.; Hebbeker, T.; Hedin, D.; Hegeman, J. G.; Heinmiller, J. M.; Heinson, A. P.; Heintz, U.; Hensel, C.; Herner, K.; Hesketh, G.; Hildreth, M. D.; Hirosky, R.; Hobbs, J. D.; Hoeneisen, B.; Hoeth, H.; Hohlfeld, M.; Hong, S. J.; Hossain, S.; Houben, P.; Hu, Y.; Hubacek, Z.; Hynek, V.; Iashvili, I.; Illingworth, R.; Ito, A. S.; Jabeen, S.; Jaffré, M.; Jain, S.; Jakobs, K.; Jarvis, C.; Jesik, R.; Johns, K.; Johnson, C.; Johnson, M.; Jonckheere, A.; Jonsson, P.; Juste, A.; Kajfasz, E.; Kalinin, A. M.; Kalk, J. R.; Kalk, J. M.; Kappler, S.; Karmanov, D.; Kasper, P. A.; Katsanos, I.; Kau, D.; Kaur, R.; Kaushik, V.; Kehoe, R.; Kermiche, S.; Khalatyan, N.; Khanov, A.; Kharchilava, A.; Kharzheev, Y. M.; Khatidze, D.; Kim, T. J.; Kirby, M. H.; Kirsch, M.; Klima, B.; Kohli, J. M.; Konrath, J.-P.; Korablev, V. M.; Kozelov, A. V.; Krop, D.; Kuhl, T.; Kumar, A.; Kunori, S.; Kupco, A.; Kurča, T.; Kvita, J.; Lacroix, F.; Lam, D.; Lammers, S.; Landsberg, G.; Lebrun, P.; Lee, W. M.; Leflat, A.; Lehner, F.; Lellouch, J.; Leveque, J.; Li, J.; Li, Q. Z.; Li, L.; Lietti, S. M.; Lima, J. G. R.; Lincoln, D.; Linnemann, J.; Lipaev, V. V.; Lipton, R.; Liu, Y.; Liu, Z.; Lobodenko, A.; Lokajicek, M.; Love, P.; Lubatti, H. J.; Luna, R.; Lyon, A. L.; Maciel, A. K. A.; Mackin, D.; Madaras, R. J.; Mättig, P.; Magass, C.; Magerkurth, A.; Mal, P. K.; Malbouisson, H. B.; Malik, S.; Malyshev, V. L.; Mao, H. S.; Maravin, Y.; Martin, B.; McCarthy, R.; Melnitchouk, A.; Mendoza, L.; Mercadante, P. G.; Merkin, M.; Merritt, K. W.; Meyer, J.; Meyer, A.; Millet, T.; Mitrevski, J.; Molina, J.; Mommsen, R. K.; Mondal, N. K.; Moore, R. W.; Moulik, T.; Muanza, G. S.; Mulders, M.; Mulhearn, M.; Mundal, O.; Mundim, L.; Nagy, E.; Naimuddin, M.; Narain, M.; Naumann, N. A.; Neal, H. A.; Negret, J. P.; Neustroev, P.; Nilsen, H.; Nogima, H.; Novaes, S. F.; Nunnemann, T.; O'Dell, V.; O'Neil, D. C.; Obrant, G.; Ochando, C.; Onoprienko, D.; Oshima, N.; Osta, J.; Otec, R.

    2008-05-01

    We present the results of a search for the production of an excited state of the electron, e*, in proton-antiproton collisions at s=1.96TeV. The data were collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 1fb-1. We search for e* in the process p pmacr →e*e, with the e* subsequently decaying to an electron plus photon. No excess above the standard model background is observed. Interpreting our data in the context of a model that describes e* production by four-fermion contact interactions and e* decay via electroweak processes, we set 95% C.L. upper limits on the production cross section ranging from 8.9 to 27 fb, depending on the mass of the excited electron. Choosing the scale for contact interactions to be Λ=1TeV, excited electron masses below 756 GeV are excluded at the 95% C.L.

  19. Vibrationally resolved electronic spectra including vibrational pre-excitation: Theory and application to VIPER spectroscopy

    Science.gov (United States)

    von Cosel, Jan; Cerezo, Javier; Kern-Michler, Daniela; Neumann, Carsten; van Wilderen, Luuk J. G. W.; Bredenbeck, Jens; Santoro, Fabrizio; Burghardt, Irene

    2017-10-01

    Vibrationally resolved electronic absorption spectra including the effect of vibrational pre-excitation are computed in order to interpret and predict vibronic transitions that are probed in the Vibrationally Promoted Electronic Resonance (VIPER) experiment [L. J. G. W. van Wilderen et al., Angew. Chem., Int. Ed. 53, 2667 (2014)]. To this end, we employ time-independent and time-dependent methods based on the evaluation of Franck-Condon overlap integrals and Fourier transformation of time-domain wavepacket autocorrelation functions, respectively. The time-independent approach uses a generalized version of the FCclasses method [F. Santoro et al., J. Chem. Phys. 126, 084509 (2007)]. In the time-dependent approach, autocorrelation functions are obtained by wavepacket propagation and by the evaluation of analytic expressions, within the harmonic approximation including Duschinsky rotation effects. For several medium-sized polyatomic systems, it is shown that selective pre-excitation of particular vibrational modes leads to a redshift of the low-frequency edge of the electronic absorption spectrum, which is a prerequisite for the VIPER experiment. This effect is typically most pronounced upon excitation of modes that are significantly displaced during the electronic transition, such as ring distortion modes within an aromatic π-system. Theoretical predictions as to which modes show the strongest VIPER effect are found to be in excellent agreement with experiment.

  20. Coherent and Tunable Terahertz Radiation from Graphene Surface Plasmon Polarirons Excited by Cyclotron Electron Beam

    Science.gov (United States)

    Zhao, Tao; Gong, Sen; Hu, Min; Zhong, Renbin; Liu, Diwei; Chen, Xiaoxing; Zhang, Ping; Wang, Xinran; Zhang, Chao; Wu, Peiheng; Liu, Shenggang

    2015-01-01

    Terahertz (THz) radiation can revolutionize modern science and technology. To this date, it remains big challenges to develop intense, coherent and tunable THz radiation sources that can cover the whole THz frequency region either by means of only electronics (both vacuum electronics and semiconductor electronics) or of only photonics (lasers, for example, quantum cascade laser). Here we present a mechanism which can overcome these difficulties in THz radiation generation. Due to the natural periodicity of 2π of both the circular cylindrical graphene structure and cyclotron electron beam (CEB), the surface plasmon polaritions (SPPs) dispersion can cross the light line of dielectric, making transformation of SPPs into radiation immediately possible. The dual natural periodicity also brings significant excellences to the excitation and the transformation. The fundamental and hybrid SPPs modes can be excited and transformed into radiation. The excited SPPs propagate along the cyclotron trajectory together with the beam and gain energy from the beam continuously. The radiation density is enhanced over 300 times, up to 105 W/cm2. The radiation frequency can be widely tuned by adjusting the beam energy or chemical potential. This mechanism opens a way for developing desired THz radiation sources to cover the whole THz frequency regime. PMID:26525516

  1. Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems

    International Nuclear Information System (INIS)

    Meer, R. van; Gritsenko, O. V.; Baerends, E. J.

    2014-01-01

    Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ω α and oscillator strengths f α for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Löwdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Löwdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Löwdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ω α (R) curves along the bond dissociation coordinate R for the molecules LiH, Li 2 , and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate

  2. Vibrational energy transfer in selectively excited diatomic molecules. [Relaxation rates, self-relaxation, upper limits

    Energy Technology Data Exchange (ETDEWEB)

    Dasch, C.J.

    1978-09-01

    Single rovibrational states of HCl(v=2), HBr(v=2), DCl(v=2), and CO(v=2) were excited with a pulsed optical parametric oscillator (OPO). Total vibrational relaxation rates near - resonance quenchers were measured at 295/sup 0/K using time resolved infrared fluorescence. These rates are attributed primarily to V - V energy transfer, and they generally conform to a simple energy gap law. A small deviation was found for the CO(v) + DCl(v') relaxation rates. Upper limits for the self relaxation by V - R,T of HCl(v=2) and HBr(v=2) and for the two quantum exchange between HCl and HBr were determined. The HF dimer was detected at 295/sup 0/K and 30 torr HF pressure with an optoacoustic spectrometer using the OPO. Pulsed and chopped, resonant and non-resonant spectrophones are analyzed in detail. From experiments and first order perturbation theory, these V - V exchange rates appear to behave as a first order perturbation in the vibrational coordinates. The rotational dynamics are known to be complicated however, and the coupled rotational - vibrational dynamics were investigated theoreticaly in infinite order by the Dillon and Stephenson and the first Magnus approximations. Large ..delta..J transitions appear to be important, but these calculations differ by orders of magnitude on specific rovibrational transition rates. Integration of the time dependent semiclassical equations by a modified Gordon method and a rotationally distorted wave approximation are discussed as methods which would treat the rotational motion more accurately. 225 references.

  3. Nanoscale and single-molecule interfacial electron transfer

    DEFF Research Database (Denmark)

    Hansen, Allan Glargaard; Wackerbarth, Hainer; Nielsen, Jens Ulrik

    2003-01-01

    Electrochemical science and technology in the 21st century have reached high levels of sophistication. A fundamental quantum mechanical theoretical frame for interfacial electrochemical electron transfer (ET) was introduced by Revaz Dogonadze. This frame has remained for four decades as a basis...... scanning tunneling microscopy (STM) and single-electron tunneling (SET, or Coulomb blockade) in electrochemical. systems directly in aqueous electrolyte solution and at room temperature. We illustrate the new theoretical formalism and its perspectives by recent cases of electrochemical SET, negative...

  4. Electron impact excitation out of the 23S metastable level of He

    International Nuclear Information System (INIS)

    Boffard, J.B.; Piech, G.A.; Lagus, M.E.; Anderson, L.W.; Chun C.L.

    1996-01-01

    Using a hollow cathode discharge as a source of He, the authors have measured absolute cross sections for electron excitation out of the 2S level of He into the n=2, 3, 4, and 5 triplet levels for energies up to 20 eV. Their results show a pattern of sharply peaked excitation functions into the n = 3, 4, and 5 3 S and 3 P levels, and comparatively broad excitation functions into the 3 D levels. The 2 3 P level has a remarkably broad excitation function, and its peak direct cross section is over 10 times the size of the next largest peak cross section observed. For energies above 20 eV, the authors use charge exchange of a fast He + beam with cesium to produce a primarily He target. This allows them to extend their measurements for selected triplet levels out to 1 keV. Their data indicate that even at this energy the excitations into the 3 3 S, 3 3 D, 4 3 D have not yet entered the Born regime. Comparisons with other theoretical calculations at low energies will be made

  5. Electronic Transport in Single Molecule Junctions: Control of the Molecule-Electrode Coupling Through Intramolecular Tunneling Barriers

    DEFF Research Database (Denmark)

    Danilov, Andrey; Kubatkin, Sergey; Kafanov, Sergey

    2008-01-01

    We report on single molecule electron transport measurements of two oligophenylenevinylene (OPV3) derivatives placed in a nanogap between gold (Au) or lead (Pb) electrodes in a field effect transistor device. Both derivatives contain thiol end groups that allow chemical binding to the electrodes....... One derivative has additional methylene groups separating the thiols from the delocalized -electron system. The insertion of methylene groups changes the open state conductance by 3-4 orders of magnitude and changes the transport mechanism from a coherent regime with finite zero-bias conductance...

  6. Optical oscillator strengths of the valence-shell excitations of atoms and molecules determined by the dipole ( γ,γ) method

    Science.gov (United States)

    Xu, Long-Quan; Liu, Ya-Wei; Xu, Xin; Ni, Dong-Dong; Yang, Ke; Zhu, Lin-Fan

    2017-07-01

    The dipole (γ,γ) method, which is the inelastic X-ray scattering operated at a negligibly small momentum transfer, has been developed to determine the absolute optical oscillator strengths of the valence-shell excitations of atoms and molecules. This new method is free from the line saturation effect, and its Bethe-Born conversion factor varies much more slowly with the excitation energy than that of the dipole (e, e) method. Thus the dipole (γ,γ) method provides a reliable approach to obtain the benchmark optical oscillator strengths of the valence-shell excitations for gaseous atoms and molecules. In this paper, we give a review of the dipole (γ,γ) method and some recent measurements of absolute optical oscillator strengths of gaseous atoms and molecules. Contribution to the Topical Issue "Atomic and Molecular Data and their Applications", edited by Gordon W.F. Drake, Jung-Sik Yoon, Daiji Kato, Grzegorz Karwasz.

  7. On the biphoton excitation of the fluorescence of the bacteriochlorophyll molecules of purple photosynthetic bacteria by powerful near IR femto-picosecond pulses

    Energy Technology Data Exchange (ETDEWEB)

    Borisov, A. Yu., E-mail: borissov@belozersky.msu.ru [Moscow State University, Belozersky Institute of Physicochemical Biology (Russian Federation)

    2011-11-15

    The authors of a number of experimental works detected nonresonance biphoton excitation of bacteriochlorophyll molecules, which represent the main pigment in the light-absorbing natural 'antenna' complexes of photosynthesizing purple bacteria, by femtosecond IR pulses (1250-1500 nm). They believe that IR quanta excite hypothetic forbidden levels of the pigments of these bacteria in the double frequency range 625-750 nm. We propose and ground an alternative triplet mechanism to describe this phenomenon. According to our hypothesis, the mechanism of biphoton excitation of molecules by IR quanta can manifest itself specifically, through high triplet levels of molecules in the high fields induced by femtosecond-picosecond laser pulses.

  8. Electron distributions of the first-row homonuclear diatomic molecules, A2

    International Nuclear Information System (INIS)

    Ramirez, B.I.; Bielefeld Univ.

    1982-08-01

    Electron momentum density contour maps of the first-row homonuclear diatomic molecules, A 2 , are obtained from near Hartree-Fock wave functions. Both the total momentum density and momentum density difference (molecule - isolated atoms) maps present trends that may be related to the binding in the molecules. These results are compared with the corresponding charge density maps in position space (Bader, Henneker and Cade 1967). (author)

  9. Electron transfer mechanism and photochemistry of ferrioxalate induced by excitation in the charge transfer band.

    Science.gov (United States)

    Chen, Jie; Zhang, Hua; Tomov, Ivan V; Rentzepis, Peter M

    2008-03-17

    The photoredox reaction of ferrioxalate after 266/267 nm excitation in the charge transfer band has been studied by means of ultrafast extended X-ray absorption fine structure (EXAFS) analysis, optical transient spectroscopy, and quantum chemistry calculations. The Fe-O bond length changes combined with the transient spectra and kinetics have been measured and in combination with ultrahigh frequency density functional theory (UHF/DFT) calculations are used to determine the photochemical mechanism for the Fe(III) to Fe(II) redox reaction. The present data and the results obtained with 266/267 nm excitations strongly suggest that the primary reaction is the dissociation of the Fe-O bond before intramolecular electron transfer occurs. Low quantum yield electron photodetachment from ferrioxalate has also been observed.

  10. Experimental and theoretical study of very-low-energy inelastic processes in electron-molecule collisions. Progress report, March 20, 1982-March 20, 1983

    International Nuclear Information System (INIS)

    Golden, D.E.; Morrison, M.

    1983-01-01

    Objectives of this research are: to determine accurate integrated and differential cross sections for low energy electron-molecule elastic scattering, excitation and ionization; to develop, implement, and test new experimental and theoretical procedures for studying low energy collision processes; and to contribute to basic understanding of a fundamental problem in atomic collision physics, the interaction of a charged particle with a non-spherical target that is rich in structure

  11. Electron impact excitation of positive ions calculated in the Coulomb-Born approximation

    International Nuclear Information System (INIS)

    Nakazaki, Shinobu; Hashino, Tasuke

    1979-08-01

    Theoretical results on the electron impact excitation of positive ions are surveyed through the end of 1978. As a guide to the available data, a list of references is made. The list shows ion species, transitions, energy range and methods of calculation for the respective data. Based on the literature survey, the validity of the Coulomb-Born approximation is investigated. Comparisons with the results of the close-coupling and the distorted-wave methods are briefly summarized. (author)

  12. Terahertz and Microwave Devices Based on the Photo-Excited Low Dimensional Electronic System

    Science.gov (United States)

    2015-03-11

    2010 12-Nov-2014 Approved for Public Release; Distribution Unlimited Final Report: Continuation: Terahertz and Microwave Devices Based on the Photo...NAME(S) AND ADDRESS (ES) U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 Terahertz , Microwaves, 2 Dimensional... Terahertz and Microwave Devices Based on the Photo-Excited Low Dimensional Electronic System Report Title This experimental project funded by the ARO

  13. Photo- and radiation chemical studies of intermediates involved in excited-state electron-transfer reactions

    International Nuclear Information System (INIS)

    Hoffman, M.Z.

    1985-01-01

    Excited-state inter- and intramolecular electron-transfer reactions lie at the heart of the most photochemical solar energy conversion schemes. The authors research, which has utilized the techniques of continuous and pulsed photolysis and radiolysis, has focused on three general aspects of these reactions involving transition metal coordination complexes and electron donor-acceptor complexes: i) the effect of solution medium on the properties and quenching of the excited states; ii) the control of the quantum yields of formation of redox products; iii) the mechanism by which reduced species interact with water to yield H 2 homogeneously and heterogeneously. EDTA is among the most popular sacrificial electron donors used in model systems. Its role is to scavenge the oxidized form of the photosensitizer in order to prevent its rapid reaction with the reduced form of the electron relay species that results from the electron-transfer quenching of the excited photosensitizer. In systems involving MV 2+ , the radicals resulting from the oxidation of EDTA can eventually lead to the generation of a second equivalent of MV + ; the reducing agent is believed to be a radical localized on the carbon atom alpha to the carboxylate group. The reaction of radiolytically-generated OH/H with EDTA produces this radical directly via H-abstraction or indirectly via deprotonation of the carbon atom adjacent to the nitrogen radical site in the oxidized amine moiety; it reduces MV 2+ with rate constants of 2.8 x 10 9 , 7.6 x 10 9 , and 8.5 x 10 6 M -1 s -1 at pH 12.5, 8.3, and 4.7, respectively. Degradative decarboxylation of EDTA-radicals and their back electron-transfer reactions are enhanced in acidic solution causing the yield of MV + to be severely diminished

  14. Probing the local environment of a single OPE3 molecule using inelastic tunneling electron spectroscopy.

    Science.gov (United States)

    Frisenda, Riccardo; Perrin, Mickael L; van der Zant, Herre S J

    2015-01-01

    We study single-molecule oligo(phenylene ethynylene)dithiol junctions by means of inelastic electron tunneling spectroscopy (IETS). The molecule is contacted with gold nano-electrodes formed with the mechanically controllable break junction technique. We record the IETS spectrum of the molecule from direct current measurements, both as a function of time and electrode separation. We find that for fixed electrode separation the molecule switches between various configurations, which are characterized by different IETS spectra. Similar variations in the IETS signal are observed during atomic rearrangements upon stretching of the molecular junction. Using quantum chemistry calculations, we identity some of the vibrational modes which constitute a chemical fingerprint of the molecule. In addition, changes can be attributed to rearrangements of the local molecular environment, in particular at the molecule-electrode interface. This study shows the importance of taking into account the interaction with the electrodes when describing inelastic contributions to transport through single-molecule junctions.

  15. Differential electron emission from polycyclic aromatic hydrocarbon molecules under fast ion impact

    OpenAIRE

    Biswas, Shubhadeep; Champion, Christophe; Tribedi, Lokesh C.

    2017-01-01

    Interaction between polycyclic aromatic hydrocarbon (PAH) molecule and energetic ion is a subject of interest in different areas of modern physics. Here, we present measurements of energy and angular distributions of absolute double differential electron emission cross section for coronene (C24H12) and fluorene (C13H10) molecules under fast bare oxygen ion impact. For coronene, the?angular distributions?of the low energy electrons are quite different from that of simpler targets like Ne or CH...

  16. NO-γ emissions from streamer discharges: direct electron impact excitation versus resonant energy transfer

    International Nuclear Information System (INIS)

    Liu Ningyu; Pasko, Victor P

    2010-01-01

    It has been established that production of NO-γ emission in pulsed corona discharges is dominated by the energy transfer from N 2 (A 3 Σ u + ) to the NO ground state NO(X 2 Π r ) while direct excitation by electron impact is negligible. However, recent studies suggest that the electron impact excitation plays a more important role. In this work, we report modelling results of NO-γ emission associated with streamer discharges using two cross section data sets available in the literature. The first set was originally reported by Mojarrabi et al (1996 Phys. Rev. A 54 2977-82) and later updated by Brunger et al (2000 J. Phys. B: At. Mol. Opt. Phys. 33 809-19); the second set was published by Hayashi (1990 Nonequilibrium Processes in Partially Ionized Gases (NATO Advanced Science Institutes Series, Series B, Physics vol 220) ed M Capitelli and J N Bardsley (New York: Plenum) pp 333-40). According to the results, the role played by the electron impact excitation in the production of NO-γ is drastically different when different cross sections are used. The results indicate that the first data set leads to better agreement with experimental measurements. (fast track communication)

  17. Distorted-wave theory of electron-ion collisions. I. Direct excitation and ionization

    International Nuclear Information System (INIS)

    Hahn, Y.

    1977-01-01

    A simple modification of the Bethe approximation for high-energy electron-atom collisions is considered for the purpose of analyzing the medium-energy scattering by highly stripped ionic targets. The effect of amplitude and phase distortions of the projectile-electron wave function on the excitation and ionization cross sections is approximately taken into account using the Elwert factor and the eikonal procedure, respectively. To facilitate the cross-section calculation further, the momentum-transfer-dependent part in the excitation matrix element is factored out in terms of an average transfer. The energy dependence of the various modification factors is studied in detail, showing that the distortion effect is large for ionic targets and decays only slowly with the scattering energy, as E/sup -1/2/. For a neutral target, however, the distortion effects roughly cancel with each other, thus resulting in the effectiveness of the unmodified Bethe cross section at much lower energies than one usually expects. The improved formalism is applied to estimate the total cross sections for the direct excitation and ionization of outer-shell electrons of the ionic target. The results are drastically changed from the unmodified Bethe approximation, and are generally in fair agreement with experimental data for all energies except in the threshold region

  18. X-ray absorption spectroscopy of the chiral molecules fenchone, α-pinene, limonene and carvone in the C1s excitation region

    Energy Technology Data Exchange (ETDEWEB)

    Ozga, Christian, E-mail: ozga@physik.uni-kassel.de [Institute for Physics and CINSaT, University of Kassel, Heinrich-Plett Str. 40, 34132 Kassel (Germany); Jänkälä, Kari [Centre for Molecular Materials Research, University of Oulu, PO Box 3000, 90014 Oulu (Finland); Schmidt, Philipp; Hans, Andreas; Reiß, Philipp; Ehresmann, Arno; Knie, André [Institute for Physics and CINSaT, University of Kassel, Heinrich-Plett Str. 40, 34132 Kassel (Germany)

    2016-02-15

    Highlights: • Determination of the X-ray absorption spectra for two terpenoids and two terpenes. • Allocation of predominant or even site-selective excitation of stereocenters. • Fragment fluorescence spectra of the prototype molecules are identical. • Presented data can be used for future fluorescence circular dichroism experiments. - Abstract: Relative ionization cross sections and fluorescence intensities as functions of the exciting-photon energy were recorded for the chiral molecules carvone, α-pinene, limonene and fenchone after excitation by monochromatized synchrotron radiation with energies of the exciting-photons between 284 eV and 289 eV. At selected exciting-photon energies dispersed fragment fluorescence spectra in the wavelength range between 365 nm and 505 nm were obtained. Time dependent density functional theory (TD-DFT) computations were performed to analyze the experimentally observed resonance-structures. Comparison of the computed and recorded spectra demonstrates the possibility of a predominant or even specific excitation of one particular stereocenter site in a molecule with more than one stereocenter.

  19. Enhancement of Curie temperature of barium hexaferrite by dense electronic excitations

    Directory of Open Access Journals (Sweden)

    Manju Sharma

    2014-07-01

    Full Text Available Curie temperature of polycrystalline barium hexaferrite (BaFe12O19, prepared by conventional solid state technique, is anomalously and significantly enhanced (by nearly 15% by energetic heavy ion irradiation (150 MeV, Ag12+ at ambient temperature due to dense electronic excitations Moderate fluence (1 × 1012 ions/cm2 induces structural defects giving rise to above enhancement. As established by X-ray diffraction, scanning electron microscopy and Raman studies, higher fluence (1 × 1013 ions/cm2 has structurally transformed the sample to amorphous phase with marginal change in magnetization and Curie temperature.

  20. Storage of Multiple Coherent Microwave Excitations in an Electron Spin Ensemble

    DEFF Research Database (Denmark)

    Wu, Hua; George, Richard E.; Wesenberg, Janus H.

    2010-01-01

    Strong coupling between a microwave photon and electron spins, which could enable a long-lived quantum memory element for superconducting qubits, is possible using a large ensemble of spins. This represents an inefficient use of resources unless multiple photons, or qubits, can be orthogonally...... stored and retrieved. Here we employ holographic techniques to realize a coherent memory using a pulsed magnetic field gradient and demonstrate the storage and retrieval of up to 100 weak 10 GHz coherent excitations in collective states of an electron spin ensemble. We further show that such collective...

  1. Excitation and ionization of ions by electron impact. Technical progress report, September 1, 1974--May 31, 1975

    International Nuclear Information System (INIS)

    Feeney, R.K.; Divine, T.F.; Kovac, R.M.; McPherson, D.; Sayle, W.E.

    1975-01-01

    This effort is devoted to experimental measurements of electron impact excitation and ionization cross sections of ions. The cross sections of interest are those of importance in the diagnostics of CTR plasmas. Current tasks include: the completion of absolute measurements of the electron impact cross sections for Rb + , Cs + , and Tl + ions; and determination of the absolute electron impact excitation cross sections for selected transitions in Li + and other He-, Li-, and Be-like ions. (U.S.)

  2. Model of daytime emissions of electronically-vibrationally excited products of O3 and O2 photolysis: application to ozone retrieval

    Directory of Open Access Journals (Sweden)

    V. A. Yankovsky

    2006-11-01

    Full Text Available The traditional kinetics of electronically excited products of O3 and O2 photolysis is supplemented with the processes of the energy transfer between electronically-vibrationally excited levels O2(a1Δg, v and O2(b1Σ+g, v, excited atomic oxygen O(1D, and the O2 molecules in the ground electronic state O2(X3Σg−, v. In contrast to the previous models of kinetics of O2(a1Δg and O2 (b1Σ+g, our model takes into consideration the following basic facts: first, photolysis of O3 and O2 and the processes of energy exchange between the metastable products of photolysis involve generation of oxygen molecules on highly excited vibrational levels in all considered electronic states – b1Σ+g, a1Δg and X3Σg−; second, the absorption of solar radiation not only leads to populating the electronic states on vibrational levels with vibrational quantum number v equal to 0 – O2(b1Σ+g, v=0 (at 762 nm and O2(a1Δg, v=0 (at 1.27 µm, but also leads to populating the excited electronic–vibrational states O2(b1Σ+g, v=1 and O2(b1Σ+g, v=2 (at 689 nm and 629 nm. The proposed model allows one to calculate not only the vertical profiles of the O2(a1Δg, v=0 and O2(b1Σg, v=0 concentrations, but also the profiles of [O2(a1Δg, v≤5], [O2 (b1Σ+g , v=1, 2] and O2(X3Σg−, v=1–35. In the altitude range 60–125 km, consideration of the electronic-vibrational kinetics significantly changes the calculated concentrations of the metastable oxygen molecules and reduces the discrepancy between the altitude profiles of ozone concentrations retrieved from the 762-nm and 1.27-µm emissions measured simultaneously.

  3. Simple molecules as benchmark systems for molecular electronics

    NARCIS (Netherlands)

    Djukić, Darko

    2006-01-01

    In society there is a constant urge to improve existing devices and the level of success is perhaps the easiest to observe in the world of electronic devices. The complexity, functionality and reliability of these machines has increased enormously, but it approaches its limits. A new giant step

  4. Electron Capture by Tetra- and di-Chlorobenzene Molecules

    DEFF Research Database (Denmark)

    Pedersen, Niels Jørgen; Anisimov, O. A.; Lozouy, V. V.

    1985-01-01

    Experiments on inhibition and anti-inhibition of Ps formation and also on optical detection of ESR spectra in squalene solutions with 1,2,4,5-C6H2Cl4 and p-C6H4Cl2 have demonstrated the presence of short-lived molecular radical-anions (products of the spur electron capture by additives), their li...

  5. Radiation effects from first principles : the role of excitons in electronic-excited processes.

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Bryan Matthew

    2009-09-01

    Electron-hole pairs, or excitons, are created within materials upon optical excitation or irradiation with X-rays/charged particles. The ability to control and predict the role of excitons in these energetically-induced processes would have a tremendous impact on understanding the effects of radiation on materials. In this report, the excitonic effects in large cycloparaphenylene carbon structures are investigated using various first-principles methods. These structures are particularly interesting since they allow a study of size-scaling properties of excitons in a prototypical semi-conducting material. In order to understand these properties, electron-hole transition density matrices and exciton binding energies were analyzed as a function of size. The transition density matrices allow a global view of electronic coherence during an electronic excitation, and the exciton binding energies give a quantitative measure of electron-hole interaction energies in these structures. Based on overall trends in exciton binding energies and their spatial delocalization, we find that excitonic effects play a vital role in understanding the unique photoinduced dynamics in these systems.

  6. Intermediate energy cross sections for electron-impact vibrational-excitation of pyrimidine

    Energy Technology Data Exchange (ETDEWEB)

    Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Ellis-Gibbings, L.; García, G. [Instituto de Física Fundamental, CSIC, Serrano 113-bis, 28006 Madrid (Spain); Nixon, K. L. [Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, Minas Gerais (Brazil); School of Biology, Chemistry and Forensic Science, University of Wolverhampton, Wolverhampton WV1 1LY (United Kingdom); Lopes, M. C. A. [Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, Minas Gerais (Brazil); Brunger, M. J., E-mail: Michael.Brunger@flinders.edu.au [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia)

    2015-09-07

    We report differential cross sections (DCSs) and integral cross sections (ICSs) for electron-impact vibrational-excitation of pyrimidine, at incident electron energies in the range 15–50 eV. The scattered electron angular range for the DCS measurements was 15°–90°. The measurements at the DCS-level are the first to be reported for vibrational-excitation in pyrimidine via electron impact, while for the ICS we extend the results from the only previous condensed-phase study [P. L. Levesque, M. Michaud, and L. Sanche, J. Chem. Phys. 122, 094701 (2005)], for electron energies ⩽12 eV, to higher energies. Interestingly, the trend in the magnitude of the lower energy condensed-phase ICSs is much smaller when compared to the corresponding gas phase results. As there is no evidence for the existence of any shape-resonances, in the available pyrimidine total cross sections [Baek et al., Phys. Rev. A 88, 032702 (2013); Fuss et al., ibid. 88, 042702 (2013)], between 10 and 20 eV, this mismatch in absolute magnitude between the condensed-phase and gas-phase ICSs might be indicative for collective-behaviour effects in the condensed-phase results.

  7. Single-molecule electronics: Cooling individual vibrational modes by the tunneling current.

    Science.gov (United States)

    Lykkebo, Jacob; Romano, Giuseppe; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C

    2016-03-21

    Electronic devices composed of single molecules constitute the ultimate limit in the continued downscaling of electronic components. A key challenge for single-molecule electronics is to control the temperature of these junctions. Controlling heating and cooling effects in individual vibrational modes can, in principle, be utilized to increase stability of single-molecule junctions under bias, to pump energy into particular vibrational modes to perform current-induced reactions, or to increase the resolution in inelastic electron tunneling spectroscopy by controlling the life-times of phonons in a molecule by suppressing absorption and external dissipation processes. Under bias the current and the molecule exchange energy, which typically results in heating of the molecule. However, the opposite process is also possible, where energy is extracted from the molecule by the tunneling current. Designing a molecular "heat sink" where a particular vibrational mode funnels heat out of the molecule and into the leads would be very desirable. It is even possible to imagine how the vibrational energy of the other vibrational modes could be funneled into the "cooling mode," given the right molecular design. Previous efforts to understand heating and cooling mechanisms in single molecule junctions have primarily been concerned with small models, where it is unclear which molecular systems they correspond to. In this paper, our focus is on suppressing heating and obtaining current-induced cooling in certain vibrational modes. Strategies for cooling vibrational modes in single-molecule junctions are presented, together with atomistic calculations based on those strategies. Cooling and reduced heating are observed for two different cooling schemes in calculations of atomistic single-molecule junctions.

  8. Ab initio structural and electronic properties of hydrogenated silicon nanoclusters in the ground and excited state

    International Nuclear Information System (INIS)

    Degoli, Elena; Bisi, O.; Ossicini, Stefano; Cantele, G.; Ninno, D.; Luppi, Eleonora; Magri, Rita

    2004-01-01

    Electronic and structural properties of small hydrogenated silicon nanoclusters as a function of dimension are calculated from ab initio technique. The effects induced by the creation of an electron-hole pair are discussed in detail, showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure after an electronic excitation of the cluster is analyzed together with the role of the symmetry constraint during the relaxation. We point out how the overall effect is that of significantly changing the electronic spectrum if no symmetry constraint is imposed to the system. Such distortion can account for the Stokes shift and provides a possible structural model to be linked to the four-level scheme invoked in the literature to explain recent results for the optical gain in silicon nanoclusters. Finally, formation energies for clusters with increasing dimension are calculated and their relative stability discussed

  9. Differential cross sections for intermediate-energy electron scattering from α-tetrahydrofurfuryl alcohol: Excitation of electronic-states

    Energy Technology Data Exchange (ETDEWEB)

    Chiari, L.; Jones, D. B.; Thorn, P. A.; Pettifer, Z. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Duque, H. V. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Departamento de Física, Universidade Federal de Juiz de Fora, Juiz de Fora, MG (Brazil); Silva, G. B. da [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001 (Australia); Universidade Federal de Mato Grosso, Barra do Garças, Mato Grosso (Brazil); Limão-Vieira, P. [Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica (Portugal); Duflot, D. [Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523, Université Lille, F-59655 Villeneuve d’Ascq Cedex (France); Hubin-Franskin, M.-J.; Delwiche, J. [Départment de Chimie, Université de Liège, Institut de Chimie-Bât. B6C, B-4000 Liège 1 (Belgium); Blanco, F. [Departamento de Física Atómica, Molecular y Nuclear, Universidad Complutense de Madrid, Madrid E-28040 (Spain); García, G. [Instituto de Física Fundamental, CSIC, Madrid E-28006 (Spain); and others

    2014-07-14

    We report on measurements of differential cross sections (DCSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol (THFA). The energy range of these experiments was 20–50 eV, while the scattered electron was detected in the 10°–90° angular range. There are currently no other experimental data or theoretical computations against which we can directly compare the present measured results. Nonetheless, we are able to compare our THFA DCSs with earlier cross section measurements for Rydberg-state electronic excitation for tetrahydrofuran, a similar cyclic ether, from Do et al. [J. Chem. Phys. 134, 144302 (2011)]. In addition, “rotationally averaged” elastic DCSs, calculated using our independent atom model with screened additivity rule correction approach are also reported. Those latter results give integral cross sections consistent with the optical theorem, and supercede those from the only previous study of Milosavljević et al. [Eur. Phys. J. D 40, 107 (2006)].

  10. Analytical formulation for modulation of time-resolved dynamical Franz-Keldysh effect by electron excitation in dielectrics

    Science.gov (United States)

    Otobe, T.

    2017-12-01

    Analytical formulation of subcycle modulation (SCM) of dielectrics including electron excitation is presented. The SCM is sensitive to not only the time-resolved dynamical Franz-Keldysh effect (Tr-DFKE) [T. Otobe et al., Phys. Rev. B 93, 045124 (2016), 10.1103/PhysRevB.93.045124], which is the nonlinear response without the electron excitation, but also the excited electrons. The excited electrons enhance the modulation with even harmonics of pump laser frequency, and generate the odd-harmonics components. The new aspect of SCM is a consequence of (i) the interference between the electrons excited by the pump laser and those excited by the probe-pulse laser and (ii) oscillation of the generated wave packed by the pump laser. When the probe- and pump-pulse polarizations are parallel, the enhancement of the even harmonics and the generation of the odd-harmonics modulation appear. However, if the polarizations are orthogonal, the effect arising from the electron excitations becomes weak. By comparing the parabolic and cosine band models, I found that the electrons under the intense laser field move as quasifree particles.

  11. The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

    KAUST Repository

    Song, Yin

    2015-06-07

    © 2015 AIP Publishing LLC. Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S (λ 1, T∼ 2, λ 3)) along the population time (T∼ 2) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S (λ 1, ν∼ 2, λ 3)). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+ ν∼ 2) in the rephasing beating map and at negative frequency (- ν∼ 2) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems.

  12. Observing electron localization in a dissociating H2+ molecule in real time.

    Science.gov (United States)

    Xu, H; Li, Zhichao; He, Feng; Wang, X; Atia-Tul-Noor, A; Kielpinski, D; Sang, R T; Litvinyuk, I V

    2017-06-16

    Dissociation of diatomic molecules with odd number of electrons always causes the unpaired electron to localize on one of the two resulting atomic fragments. In the simplest diatomic molecule H 2 + dissociation yields a hydrogen atom and a proton with the sole electron ending up on one of the two nuclei. That is equivalent to breaking of a chemical bond-the most fundamental chemical process. Here we observe such electron localization in real time by performing a pump-probe experiment. We demonstrate that in H 2 + electron localization is complete in just 15 fs when the molecule's internuclear distance reaches 8 atomic units. The measurement is supported by a theoretical simulation based on numerical solution of the time-dependent Schrödinger equation. This observation advances our understanding of detailed dynamics of molecular dissociation.

  13. Resonances in electron-molecule scattering and photoionization

    International Nuclear Information System (INIS)

    Schneider, B.I.; Collins, L.A.

    1984-05-01

    The development of reliable theoretical models for calculating the decay of quasi-stationary states of molecular systems has become an important endeavor for theoretical chemists. The understanding and analysis of a wide variety of physical and chemical phenomena depend on a knowledge of the behavior of these states in both collisional and photoionization problems. In this article we describe the theory and calculation of these cross sections using our Linear Algebraic/Optical Potential method. The theory makes optimal use of the numerical methods developed to solve large sets of coupled integral equations and the bound state techniques used by quantum chemists. Calculations are presented for a representative class of diatomic and triatomic molecules at varying levels of sophistication and for collisional and photoionization cross sections. 48 references, 11 figures

  14. Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations

    Science.gov (United States)

    Matthews, Edward; Cercola, Rosaria; Mensa-Bonsu, Golda; Neumark, Daniel M.; Dessent, Caroline E. H.

    2018-02-01

    Laser photodissociation spectroscopy of the I-.thymine (I-.T) and I-.cytosine (I-.C) nucleobase clusters has been conducted for the first time across the regions above the electron detachment thresholds to explore the excited states and photodissociation channels. Although photodepletion is strong, only weak ionic photofragment signals are observed, indicating that the clusters decay predominantly by electron detachment. The photodepletion spectra of the I-.T and I-.C clusters display a prominent dipole-bound excited state (I) in the vicinity of the vertical detachment energy (˜4.0 eV). Like the previously studied I-.uracil (I-.U) cluster [W. L. Li et al., J. Chem. Phys. 145, 044319 (2016)], the I-.T cluster also displays a second excited state (II) centred at 4.8 eV, which we similarly assign to a π-π* nucleobase-localized transition. However, no distinct higher-energy absorption bands are evident in the spectra of the I-.C. Time-dependent density functional theory (TDDFT) calculations are presented, showing that while each of the I-.T and I-.U clusters displays a single dominant π-π* nucleobase-localized transition, the corresponding π-π* nucleobase transitions for I-.C are split across three separate weaker electronic excitations. I- and deprotonated nucleobase anion photofragments are observed upon photoexcitation of both I-.U and I-.T, with the action spectra showing bands (at 4.0 and 4.8 eV) for both the I- and deprotonated nucleobase anion production. The photofragmentation behaviour of the I-.C cluster is distinctive as its I- photofragment displays a relatively flat profile above the expected vertical detachment energy. We discuss the observed photofragmentation profiles of the I-.pyrimidine clusters, in the context of the previous time-resolved measurements, and conclude that the observed photoexcitations are primarily consistent with intracluster electron transfer dominating in the near-threshold region, while nucleobase-centred excitations

  15. Ion and electron swarm studies of relevance to plasma processing: positive ion-molecule and electron-molecule studies of SF6 and derivatives

    International Nuclear Information System (INIS)

    Atterbury, C.; Kennedy, R.A.; Critchley, A.D.J.; Mayhew, C.A.

    2002-01-01

    Many sequential and parallel chemical reactions involving charged species occur in a plasma. Data needed to model plasma's chemical and physical environment includes cross-section, rate coefficients, and product ion distribution of electron-molecule and ion-molecule processes. Such reactions are studied by our group away from the complexity of the plasma environment, with experimental techniques that allow us to concentrate on a single process, where usually only one or two species are involved. A molecule commonly used in plasma etching applications is SF 6 1,2 . We have performed a series of positive ion-molecule and electron attachment studies on SF 6 and related molecules, including SeF 6 , TeF 6 (i.e. XF 6 molecules), SF 5 CF 3 and SF 5 Cl (i.e. SF 5 X molecules) 3- (. The studies of ion reactions with and electron attachment to SF 6 and physically similar molecules are of value when seeking to understand the ion and electron chemistry occurring in SF 6 containing plasma. The result of these studies are presented in this poster. Ion-molecule reactions. Rate coefficients and ion product branching ratios have been determined with the Selected Ion Flow Tube (SIFT) at room temperature (300 K) for reactions of SF 5 X with the following twenty-two cations; Ne + , F + , Ar + , N 2 + , N + , CO + , CO 2 + , O + , N 2 O + , O 2 + , SF 4 + , CF 2 + , SF + , SF 2 + , NO 2 + , SF 5 + , NO + , CF + , CF 3 + , SF 3 + , and H 3 O + (listed in order of decreasing recombination energy). SF 2 + , NO 2 + , NO + , SF 3 + , and H 3 O + are found to be unreacted with both SF 5 CF 3 and SF 5 Cl. The majority of the other reactions proceed with rate coefficients that are close to the capture value. Those found to occur at rates significantly less than the capture mechanism value re the reactions of O 2 + , SF + , SF 5 + , and CF 3 + with SF 5 CF 3 , and SF 4 + and SF 5 + with SF 5 Cl. Several distinction processes are observed among the large number of reactions studied, including

  16. Controlling electron-electron correlation in frustrated double ionization of triatomic molecules with orthogonally polarized two-color laser fields

    Science.gov (United States)

    Chen, A.; Kling, M. F.; Emmanouilidou, A.

    2017-09-01

    We demonstrate the control of electron-electron correlation in frustrated double ionization (FDI) of the two-electron triatomic molecule D3 + when driven by two orthogonally polarized two-color laser fields. We employ a three-dimensional semiclassical model that fully accounts for the electron and nuclear motion in strong fields. We analyze the FDI probability and the distribution of the momentum of the escaping electron along the polarization direction of the longer wavelength and more intense laser field. These observables, when considered in conjunction, bear clear signatures of the prevalence or absence of electron-electron correlation in FDI, depending on the time delay between the two laser pulses. We find that D3 + is a better candidate than H2 for demonstrating also experimentally that electron-electron correlation indeed underlies FDI.

  17. Breaking Symmetry in Time-Dependent Electronic Structure Theory to Describe Spectroscopic Properties of Non-Collinear and Chiral Molecules

    Science.gov (United States)

    Goings, Joshua James

    Time-dependent electronic structure theory has the power to predict and probe the ways electron dynamics leads to useful phenomena and spectroscopic data. Here we report several advances and extensions of broken-symmetry time-dependent electronic structure theory in order to capture the flexibility required to describe non-equilibrium spin dynamics, as well as electron dynamics for chiroptical properties and vibrational effects. In the first half, we begin by discussing the generalization of self-consistent field methods to the so-called two-component structure in order to capture non-collinear spin states. This means that individual electrons are allowed to take a superposition of spin-1/2 projection states, instead of being constrained to either spin-up or spin-down. The system is no longer a spin eigenfunction, and is known a a spin-symmetry broken wave function. This flexibility to break spin symmetry may lead to variational instabilities in the approximate wave function, and we discuss how these may be overcome. With a stable non-collinear wave function in hand, we then discuss how to obtain electronic excited states from the non-collinear reference, along with associated challenges in their physical interpretation. Finally, we extend the two-component methods to relativistic Hamiltonians, which is the proper setting for describing spin-orbit driven phenomena. We describe the first implementation of the explicit time propagation of relativistic two-component methods and how this may be used to capture spin-forbidden states in electronic absorption spectra. In the second half, we describe the extension of explicitly time-propagated wave functions to the simulation of chiroptical properties, namely circular dichroism (CD) spectra of chiral molecules. Natural circular dichroism, that is, CD in the absence of magnetic fields, originates in the broken parity symmetry of chiral molecules. This proves to be an efficient method for computing circular dichroism spectra

  18. Materials Meets Concepts in Molecule-Based Electronics

    KAUST Repository

    Ortmann, Frank

    2014-10-14

    In this contribution, molecular materials are highlighted as an important topic in the diverse field of condensed matter physics, with focus on their particular electronic and transport properties. A better understanding of their performance in various applications and devices demands for an extension of basic theoretical approaches to describe charge transport in molecular materials, including the accurate description of electron-phonon coupling. Starting with the simplest case of a molecular junction and moving on to larger aggregates of bulk organic semiconductors, charge-transport regimes from ballistic motion to incoherent hopping, which are frequently encountered in molecular systems under respective conditions, are discussed. Transport features of specific materials are described through ab initio material parameters whose determination is addressed. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.

  19. Observation of Electronic Excitation Transfer Through Light Harvesting Complex II Using Two-Dimensional Electronic-Vibrational Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, NHC; Gruenke, NL; Oliver, TAA; Ballottari, M; Bassi, R; Fleming, GR

    2016-10-05

    Light-harvesting complex II (LHCII) serves a central role in light harvesting for oxygenic photosynthesis and is arguably the most important photosynthetic antenna complex. In this article, we present two-dimensional electronic–vibrational (2DEV) spectra of LHCII isolated from spinach, demonstrating the possibility of using this technique to track the transfer of electronic excitation energy between specific pigments within the complex. We assign the spectral bands via comparison with the 2DEV spectra of the isolated chromophores, chlorophyll a and b, and present evidence that excitation energy between the pigments of the complex are observed in these spectra. Lastly, we analyze the essential components of the 2DEV spectra using singular value decomposition, which makes it possible to reveal the relaxation pathways within this complex.

  20. Tuning the Electronic and Dynamical Properties of a Molecule by Atom Trapping Chemistry.

    Science.gov (United States)

    Pham, Van Dong; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Abad, Enrique; Dappe, Yannick J; Smogunov, Alexander; Lagoute, Jérôme

    2017-11-28

    The ability to trap adatoms with an organic molecule on a surface has been used to obtain a range of molecular functionalities controlled by the choice of the molecular trapping site and local deprotonation. The tetraphenylporphyrin molecule used in this study contains three types of trapping sites: two carbon rings (phenyl and pyrrole) and the center of a macrocycle. Catching a gold adatom on the carbon rings leads to an electronic doping of the molecule, whereas trapping the adatom at the macrocycle center with single deprotonation leads to a molecular rotor and a second deprotonation leads to a molecular jumper. We call "atom trapping chemistry" the control of the structure, electronic, and dynamical properties of a molecule achieved by trapping metallic atoms with a molecule on a surface. In addition to the examples previously described, we show that more complex structures can be envisaged.